Because he is weak and/or an idiot. To use Misty's list and off set her answers - please read the two posts together...
he is too childish to understand his commitment
he wants his cake without understanding the responsibilities
he doesn't know how to connect with his wife - but then neither does she
he cops out, gives up on his vows and decides he has a "right"
he prefers to take the lazy way out and is reactionary