"This sometimes takes place when, for example, there are many women who, as they get older, find it increasingly difficult to marry. In this case a woman opts for a husband who is not able to fulfil the normal marital duties like
financial maintenance, or spending adequate time with her, for example. She considers that marrying such a husband is better than remaining unmarried."
But how can be this legal.

Its in Qur'an written clearly the men needs to treat his wive equally(the same treatment)and he needs to be the women protector, so he needs to ensure some financial maintenance to her too.