The straightforward answer: you can do a lot more with an interest, and use social reinforcement to your advantage, if you're plugged into an institution. Trying to go it alone is a serious challenge: you're isolated, you'll have motivation problems, you'll have a higher probability of getting yourself into eccentric dead ends if you don't have guidance.

Also, a lot of people really care what others think of them. We seem to disapprove of that on LessWrong, but I don't see why it's any more selfish or venal to want approval than to want money.