I never cheated while I had a spouse. But I will say they is nothing more exciting than the first time you are with someone new. I can see someone bring intoxicated by that.
Pretty sure that my ex wanted out and was too chickenshit to be honest or direct about it so he leapt at the chance of having an affair when it presented itself and was deliberately careless in the hope I’d catch him and end our marriage. That didn’t work so he had to come clean but even then he never said he wanted our marriage to be over. I had to be the one to say those words (and then he cried :rolleyes: ).
Don’t get me wrong, all the other stuff people have said are part of it - the thrill of the new and the forbidden particularly. I just think he was also hoping to get out of telling me our marriage was over by “accidentally” being caught. I base this on his paramour telling me afterwards that he kept saying things like “Can you imagine what would happen if she walked in and caught us now? I wish she would”.
People cheat 'cause there just aren’t any nice guys (or gals) out there anymore.
I cheated on a bf because he kept accusing me of it and I figured if I had to listen to all that bullshit I may as well deserve it.
Then I broke up with him.
You always were a silver tongued devil 
Maybe a better question is why wouldn’t you? If tapping that new ass really means that much more than some implied promise of fidelity you made years ago, then why lock yourself in some ideological prison of your own making? Just be prepared to accept the consequences.
Someone give this man a psychology degree.
Seriously, I think that however much a man loves his partner, when he gets married (or thinks about getting married) a little part of his brain is still screaming in terror: "Hey! What are you doing, you dickhead? You realise that from now on you will only ever have sex with one person for the rest of your damn life? One. Do you realise how many women there are in the world? And you want to limit yourself to ONE?
You are generalizing from a sample of one here. The reason you personally are more successful with married women might be because you project a wham-bam-thank-you-ma’am vibe, which would be more attractive to married convention goers.
I cheat not.
They think it’s worth getting caught or they think they won’t get caught; either way they think it will benefit them more than not doing it.
People cheat because sex.
Now, ‘sex’ delivers different things to different people, so it just depends on the person.
But it’s always sex. Yes, even for women. 
That wife you can’t get into bed more than once a month would probably hit someone else in a minute. It’s just human nature.