Obviously the rest of the team is likely to be very talented as well. Also, he's the founder, which includes a responsibility to act in the best interest of the company (plus $20M/yr would be much less money).
Also, someone like Bret is very unlikely to be attracted by purely monetary gain like a $20/mil year salary(or even $50/mil year.) He probably cares as much, if not more, in being able to achieve some larger goal--which requires building a sort of team he has already built.