On one level, it's more enjoyable to do work that's aligned with your values. That gives you "self-actualization" points in the ol' pyramid.
But on another level, either because you're getting equity, or because you'd like to stay employed for a while, "believing" in the company is a shorthand for saying you think that the company is going to succeed, so that your equity is worth more, or so that you don't find yourself out of a job on someone else's schedule.
But on another level, either because you're getting equity, or because you'd like to stay employed for a while, "believing" in the company is a shorthand for saying you think that the company is going to succeed, so that your equity is worth more, or so that you don't find yourself out of a job on someone else's schedule.