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?

What people want in life often comes from what they experienced themselves previously. You mentioned charity. I've put 13 years of my life into being a scouts group leader, organizimg weekly meetups, many events and multiple scout camps a year. I'm very passionate about this, since I've got so much out of being a scout since I was 7, growing up with a community, that was meaningful and not harsh and punishing as school. I wanted tp give these experience back to the next scout generation. And during my time as scout group leader I could grew even more, making my own life better through helping others. Soon I will shift my focus away from the scouts (currently its too much together with work; also I want kids soon).

I'm not saying, that you need to do this. I just wanted to explain where my motivation comes from. I get a sense of fulfilment and I'm proud of what I've done and I'm proud of the kids, that I saw growing up and now being group leaders themselves.

Finding something, that you are passionate about is very important. It doesn't need to include external responsibilities. Taking responsibility for your own self, like putting in hard work to learn a new skill, can be as fulfilling as the above.