Have you read about ashab e suffa? Prophet PBUH established madrassa at his own time to teach, so again this is something we can find in the Sunnah of Prophet PBUH.
Your other examples are related to worldly matters and that have no impact on Shariah. Anything which does not have an impact on shariah is not bidah and we both agree on that definition.
Now how does celebrating Prophet PBUH's birthday affect Shariah, let's look at this from fiq point of view.
In my previous post we discussed 5 possible categories of bidah per Sunnit scholars. Now Mawlid is either wajib (obligatory), or mandub (recommended) or permissible (mubah), or makruh (disliked) or muharram (unlawful). It is not wajib by consensus and nor is it mandub (recommended), because the reality of the mandub is "that (whose performance) the Shariah has requested but without any censure for the one who leaves it." But we see that the Shariah has not granted permission for this, and the Companions never did it and nor the Tabi'un and nor the religious (devoted) scholars - as far as I know. And it is not permissible that it should be mubah (permitted), because innovating in the religion is not permissible by consensus of the Muslims.
Hence, there is nothing left except for it to be either makruh (disliked) or haram (unlawful).
Let's now look how people celebrate it.
Some people simply make it an occasion to gather and read the story of the Mawlid, then they present speeches and Qaseedahs (songs) on this occasion. Others prepare food and refreshments to serve to the people present. Yet others hold these celebrations in the mosques, and some of them hold them in their houses.
Some people however transcend the boundaries by engaging in Haram (unlawful) and reprehensible things, such as free mixing of men and women, dancing and singing, or committing actions of Shirk such as seeking the help of the Prophet PBUH, calling upon him, seeking his support against their enemies and so on.
If this is not enough to be call it haram then let's look at few other reasons:
Imitation of the Kuffar
Celebrating the birthday of the Prophet PBUH is an imitation of the Christians, because they celebrate a day they chose as the birth of the Prophet Essa (Jesus) PBUH. Imitating them is extremely Haram. The Hadith tells us that it is forbidden to imitate the non-believers and we are commanded to differ from them.
Prophet Muhammad PBUH said:
Quote:
Whoever imitates a people is one of them (reported by Ahmad, 2/50; Abu Dawood, 4/314).
And he said:
Quote:
Be different from the Mushrikeen(Reported by Muslim, 1/222, no. 259)
This is especially with regard to things that are the symbols or rituals of their religion.
Causes Exaggeration that May Lead to Worship
Besides being Bidah and an imitation of the Christians, both of which are Haram, celebrating the birthday of the Prophet PBUH is also a means that leads to exaggeration and excess in venerating him, which even goes as far as calling upon him (making Du’a’ i.e., supplicating to him) and seeking his help, instead of calling upon Allah. This is commonly seen among many of those who observe the Bidah of the Mawlid, when they call upon the Messenger PBUH instead of Allah, and ask him for support, and sing Qaseedahs (odes) of Shirk praising him. This is again close to Christians who made their Prophet God.
We can only get close to Allah by following Sunnah:
None can get close to Allah by acts of worship which were not performed by the Prophet PBUH, his companions and the four righteous Caliph that succeeded him. If that was the case then Christian also love God and they do many things at the name of God, will those be accepted? Legislating acts of worship that the Prophet PBUH and his people never did upon the Ummah is accusing the Prophet of hiding knowledge. If there was any virtue in celebrating the Prophet’s birthday, he would not have hidden that from his companions.
It is because of celebrating such innovations that we find Muslims in a state of mess in Pakistan and India. Below are links to few videos, first two show clear shirk done by so called Hanafi Muslims in Pakistan, last video is response by Abdul Raheem Green when someone said Pakistan is a Muslim country.
https://youtu.be/_YG2oFNc6JU
https://youtu.be/Tqhe7vyKVzw
https://youtu.be/aruJaYHu6nM
Finally I should probably ask you if you are Brelvi or Deubandi? Deubandi Hanafi Muslims don't support celebration of Prophet Muhammad PBUH's birthday, however, Brelvies do and most of the shirk in the videos is done by brelvi Muslims.
Below are some links to the videos specific to Mawlid, watch and tell me if this is only Bidah or is it shirk? Anyone in right mind can see why bidah like this leads to hell fire....
https://youtu.be/gwBDB_iRRSw
https://youtu.be/ZPh88eu9HDc
https://youtu.be/Q-J8L2ynVfw
https://youtu.be/R0M-eoZt9I4
https://youtu.be/XVxrUZJTUXE
https://youtu.be/tmoDEXtRpE4
https://youtu.be/COvuH-2-xlE
Seriously this is not the Islam which I know. May Allah save us from Bidah and keep us on the right path. Ameen!