While it’s true that it’s not their duty to look after the inlaws, from what I’ve seen/heard, these types of issues tend to come up in a joint family setting. If they’re benefitting from the efforts of others, then it only makes sense that they should also contribute something.
Of course there are cases where it might not be fair, as in making her do everything all the time. As to why girls don’t exercise their rights are per Islam, well, I can guess a few reasons:
They don’t know.
They don’t care.
They’re not practicing anyway, so if they were to bring up their rights, they wouldn’t be taken seriously.
Difficult to muster up the courage in their current environment and go against what is expected of them.