As someone who works (hard) in the part of finance you're describing, it's a mix of a few things. From a purely intellectual standpoint, it's a very hard, very interesting quantitative/modeling problem to solve (ie. predict the price N seconds in the future is non-trivial). It's an extremely competitive field (you vs. other teams like you in the world competing for a slice of the pie), and you get results back from your experiments very quickly, so you know exactly where you stand. And finally, to your following point --

>Also, I'm unable to make myself do work if I don't see it contributing to some greater vision or cause

This simply is not something I experience. I've never felt any particular satisfaction from that particular aspect of a job, it's just something that never crosses my mind and incentive me in any way.