Familial generosity only extends so far.
It’s only natural to want to treat your relatives now and again. In fact, if you have an income and a decent relationship and you aren’t doing that, people might start looking at you like you have some kind of problem. Even small gestures can go a long way in terms of shoring up goodwill between family members. With the ups and downs that come with life, you never know when you might need to rely on it.
There are plenty of families that contain people who seem to freeload off their relatives at every opportunity they get, and it comes to a point where this starts to cause issues. It is inevitable that resentment is going to build among those who always find themselves paying for everything, no matter what. There comes a time when you have to make a contribution.
The trouble with spending a lot of time allowing other people to pay your way is that when they reach their limit, it may cost you more money (and more than just money). Those who value their relationships with their family are usually going to offer to make a financial contribution every so often.