Obviously, there are a lot of different reasons, but I think one that might get overlooked in modern America is the old-fashioned dynastic urge that highly successful men are especially prone to. Think of Sean Connery waxing dynastic near the end of The Man Who Would Be King. That this woman is the one worthy of commingling her genes with mine and bearing the sons who will carry forward my name, bringing satisfaction to my old age as their sons have done for Archie Manning and Ken Griffey Sr. Also, I probably won't be around that much while my kids are growing up, but she looks like she can handle it on her own.
The same kind of thinking helps explain the semi-pro skankiness of Tiger's list. Many have asked why Tiger wasn't cheating with somebody more of a rival to his wife. But there's a certain logic to aiming low to keep the peace around the house: Jamie Grubbs isn't a plausible threat to Elin Nordegren Woods to displace her as a second Mrs. Woods, while, say, Zooey Deschanel would be. (Tiger's problem is that the low quality got lost in the high quantity.)
Marrying a formidable woman can be expensive when it comes to the divorce settlement, however.