I am betting on the theory that entrepreneurship itself provides much more space for creativity than most other professions and if you succeed, you'll have a lot of money and time to pursue creativity full time. I have also read about a lot of successful entrepreneurs who discovered that they really need a startup to give direction to their creativity. Thus, serial entrepreneurs are born.
pg is one of the few entrepreneurs I can think of who didn't become a serial entrepreneur in the traditional meaning of the word but still found great outlets for their creativity. Although, at least one of pg's outlets - YCombinator can be thought of as a startup.