Married men are disposable. You get the sex and the attention but none of the crap that comes with having them around more consistently.

The wife is rarely ever thought of. She's of no consequence. The idea that it's female competition is something men tell themselves to mollify the fact that they're allowing themselves to be used.

Another aspect of it is that it's the only way a woman can pursue a man and stand a chamce of not being labeled a slut. Because it has to be kept secret or the man suffers. Take that away, and men brag. So, it's a lot like a dog chasing a car. You want the thrill of the chase, but the last thing you want or need is to actually catch one.