The best way to understand this Hadith, as with anything, is from the Qur'an itself.
Bismillahi-Rahmanir-Raheem
Satan will be the one who will mislead everyone. He will mislead many, and few will be left who will be guided. These verses give a sense of how easy it is to go astray from Satan. Read them carefully.
7:16 (Iblis) said: "Because You have sent me astray, surely I will sit in wait against them (human beings) on Your Straight Path.
7:17 "Then I will come to them from before them and behind them, from their right and from their left, and You will not find most of them as thankful ones (i.e. they will not be dutiful to You)."
7:18 (Allah) said (to Iblis): "Get out from this (Paradise), disgraced and expelled. Whoever of them (mankind) will follow you, then surely I will fill Hell with you all."
11:116 If only there had been among the generations before you persons having wisdom, prohibiting (others) from Al-Fasad (disbelief, polytheism, and all kinds of crimes and sins) in the earth, (but there were none) - except a few of those whom We saved from among them! Those who did wrong pursued the enjoyment of good things of (this worldly) life, and were Mujrimun (criminals, disbelievers in Allah, polytheists, sinners).
11:117 And your Lord would never destroy the towns wrongfully, while their people were right-doers.
11:118 And if your Lord had so willed, He could surely have made mankind one Ummah [nation or community (following one religion i.e. Islam)] but they will not cease to disagree.
11:119 Except him on whom your Lord has bestowed His Mercy (the follower of truth - Islamic Monotheism) and for that did He create them. And the Word of your Lord has been fulfilled (i.e. His Saying): "Surely, I shall fill Hell with jinn and men all together."
15:39 [Iblis (Satan)] said: "O my Lord! Because you misled me, I shall indeed adorn the path of error for them (mankind) on the earth, and I shall mislead them all.
15:40 "Except Your chosen, (guided) slaves among them."
15:41 (Allah) said: "This is the Way which will lead straight to Me."
15:42 "Certainly, you shall have no authority over My slaves, except those who follow you of the Ghawun (Mushrikun and those who go astray, criminals, polytheists, and evil-doers).
15:43 "And surely, Hell is the promised place for them all.
As for the large number of disbelievers going to Hell and so few believers going to Heaven, the Qur'an gives a sense of this in many parts where it says how very few people believe in Allah compared with a large number of people who are disbelievers:
2:83 And (remember) when We took a covenant from the Children of Israel, (saying): Worship none but Allah (Alone) and be dutiful and good to parents, and to kindred, and to orphans and Al-Masakin (the poor), and speak good to people [i.e. enjoin righteousness and forbid evil, and say the truth about Muhammad صلى الله عليه وسلم], and perform As-Salat (Iqamat-as-Salat), and give Zakat. Then you slid back, except a few of you, while you are backsliders. (Tafsir Al-Qurtubi).
2:246 Have you not thought about the group of the Children of Israel after (the time of) Musa (Moses)? When they said to a Prophet of theirs, "Appoint for us a king and we will fight in Allah's Way." He said, "Would you then refrain from fighting, if fighting was prescribed for you?" They said, "Why should we not fight in Allah's Way while we have been driven out of our homes and our children (families have been taken as captives)?" But when fighting was ordered for them, they turned away, all except a few of them. And Allah is All-Aware of the Zalimun (polytheists and wrong-doers).
2:249 Then when Talut (Saul) set out with the army, he said: "Verily! Allah will try you by a river. So whoever drinks thereof, he is not of me, and whoever tastes it not, he is of me, except him who takes (thereof) in the hollow of his hand." Yet, they drank thereof, all, except a few of them. So when he had crossed it (the river), he and those who believed with him, they said: "We have no power this day against Jalut (Goliath) and his hosts." But those who knew with certainty that they were going to meet Allah, said: "How often a smallgroup overcame a mighty host by Allah's Leave?" And Allah is with As-Sabirun (the patient).
4:46 Among those who are Jews, there are some who displace words from (their) right places and say: "We hear your word (O Muhammad صلى الله عليه وسلم and disobey," and "Hear and let you (O Muhammad صلى الله عليه وسلم) hear nothing." And Ra'ina with a twist of their tongues and as a mockery of the religion (Islam). And if only they had said: "We hear and obey", and "Do make us understand," it would have been better for them, and more proper; but Allah has cursed them for their disbelief, so they believe not except a few.
4:83 When there comes to them some matter touching (public) safety or fear, they make it known (among the people); if only they had referred it to the Messenger or to those charged with authority among them, the proper investigators would have understood it from them (directly). Had it not been for the Grace and Mercy of Allah upon you, you would have followed Shaitan (Satan), save a few of you.
11:40 (So it was) till when Our Command came and the oven gushed forth (water like fountains from the earth). We said: "Embark therein, of each kind two (male and female), and your family - except him against whom the Word has already gone forth - and those who believe. And none believed with him, except a few."
11:116 If only there had been among the generations before you persons having wisdom, prohibiting (others) from Al-Fasad (disbelief, polytheism, and all kinds of crimes and sins) in the earth, (but there were none) - except a few of those whom We saved from among them! Those who did wrong pursued the enjoyment of good things of (this worldly) life, and were Mujrimun (criminals, disbelievers in Allah, polytheists, sinners).
17:62 [Iblis (Satan)] said: "See this one whom You have honoured above me, if You give me respite (keep me alive) to the Day of Resurrection, I will surely seize and mislead his offspring (by sending them astray) all but a few!"
26:54 (Saying): "Verily these indeed are but a small band.
34:13 They worked for him as he desired, (making) high rooms, images, basins as large as reservoirs, and (cooking) cauldrons fixed (in their places). "Work you, O family of Dawud (David), with thanks!" But few of My slaves are grateful.
38:24 [Dawud (David)] said (immediately without listening to the opponent): "He has wronged you in demanding your ewe in addition to his ewes. And, verily, many partners oppress one another, except those who believe and do righteous good deeds, and they are few." And Dawud (David) guessed that We have tried him and he sought Forgiveness of his Lord, and he fell down prostrate and turned (to Allah) in repentance.
Obviously the above Hadith means that very few would be guided and many would be misguided, that is what the numbers show. But what is important is knowing why that is the case. Satan would succeed in misleading many because people easily fall into his hands considering he comes from all directions to mislead.
Allah has stressed often in the Qur'an, as you can see, how very few people actually believe in His message. This is only the start to knowing why so few people believe. In every nation in the past, there were Prophets. Except for Jonah's (as) nation, no other nation is mentioned in the Qur'an as having escaped punishment. And when those punishments came, a very small number of people believed in their Prophet.
There is another Hadith which shows the Holy Prophet (saw) who described seeing the Prophets of the past with their followers, some with a few, others with three, two or one. Some had none. Then he saw Musa (as) and his followers who were in large number, then he saw the Muslims as so many that they extended into the horizon. But how many people in history so far have been Muslim? The number is comparatively small. Billions of people are disbelievers still. There are always a large number of disbelievers in the world, and if the believers are many, they will still be there.
So if it amazes you how few get into Heaven, then remember these details and it will make more sense to you. I found my answer to this puzzle from the Qur'an as I presented it to you now. I hope it makes sense.
mg: