Some differences between marriage and those contracts you mentioned...
* they have performance requirements * they aren't life long commitments
If you don't perform well as a CEO the board can fire you. And you don't get to keep half of their personal net worth either.
You make a valid point that when things are tough, marriage helps you stay together. But it seems like for the wrong reason (fear of divorce, rather than love of the person).
It also seems likely that if the other person know's it's difficult for you to leave, they may not try as hard.
This same problem exists when professors get tenure, when you sign a 2 year contract with AT&T, or any long term contract that locks you in.