Because intellectual community is extremely hard to get. Unless you're moving to Ithaca, it's hard to find a place that is full of interesting people and ideas. This pushes you in ways you wouldn't get in places like Buffalo and so on - the culture of a city like San Francisco or Boston is full of smart people with a certain background (i.e., people who are interested in tech) who can stimulate you. You're far more likely to overhear a conversation about Claude Shannon or minimum spanning trees in SF than you are in Buffalo.