It doesn't. Looking the other members of the board in the eye and telling them you couldn't find anyone in the world more qualified for one of the most important jobs at YOUR company - responsible for hiring and firing the CEO - than your girlfriend or wife based on no other parameters should stop you from doing that. I'd imagine you'd have a difficult time raising money too - let alone the publicity.

The law doesn't stop me from running each board meeting in the form of interpretive dance, either. As a board member, I would likely seek to fire that founder immediately in either case.