Why do people around me tend to increase their responsibility load (i.e. have children, become a manager, do charity, etc.) while I (30M) try to avoid it as much as I can?

There as a time when you were very young that tying your shoes was impossible for you. For a time, your parents tied your shoes for you. Then you learned how, with difficulty, to do it yourself. Within a short time you mastered it and you don't even think about it now. You simply benefit from having tied shoes without having to ask anyone. Somewhere out there is a person that doesn't know how to tie their own shoes asking why people learned to do so for themselves, where you have that answer for yourself.

Others around you see benefits to raising children, the challenge and pay of rising in job role, or the noble contribution of doing charity work bettering others/society. For you, you don't see any of the benefits to yourself that come from those thing. Yet those other people learned to tie their shoes themselves too. You are like them in that they had the desire to better themselves in that small way because you all saw a benefit.

It sounds like the question before you is to examine your life, decide if there is anything you want in it that you don't have, and work a path to getting that. The one further thing I would recommend is don't just look at your life as it is now at age 30. Imagine your life at 35,40, 50, 65, and 80. With the versions of yourself at those ages be satisfied with the person you are today with what you know and have? Will you, at some distant year, be sad that you passed on an opportunity to have something else in your life you don't have today? If so, its up to you, today, to make the choices that will eventually make you into the person you want to be for that distant age.

Only you can answer this question and there is no wrong answer as long as you are true to yourself and have properly explored yourself and the world to properly answer this question.