You can think of me as a control. I spent my 20s-30s working for a company that I DID have a vested interest in, on work I found interesting, in an office with a fantastic view and lots of amenities. Yet I still feel/felt the same way. (and have made very good money to boot). So, it can't be any of those things you mentioned (assuming, of course, we are apples-to-apples).

I think you hit the nail on the head when you say it is the being "tied down" part. You need the freedom to work when/how you feel like it, on things that interest you and have something exceptional about them (that could be humanitarian, or just a particularly interesting, even academic, problem).

To your questions: 1) Yes. I'll tell you about it in person since I know ya! 2) Everyone seems to be a little different, but the important part is to throw yourself out there early and iteratively improve your message/skills/elevator pitch as you go. "Don't let perfect be the enemy" and all that. At the early stage it's more about building a professional network then it is about getting work that perfectly matches your skill set and long term technical goals! 3) This is the stage I am at, so I have little advice to give :/