They want to keep their jobs. I think at this point people are becoming knowledgeable enough that going against the odds like that is no longer the "safe" play as far as perception. But people aren't knowledgeable enough yet where doing something against the odds like that really hurts you the way it should.
Still amazing to me that coaches didn't figure out on their own that moving the ball from their 40 to the opponents 25 isn't a big of enough gain to give up on keeping possession.