Cuckoldry isnt a phenomena because of evolution. Its just a response to how these people cope with trauma.
Some people get cheated on and instead of resolving the trauma they accept it as part of their lives, try to justify it with being a "fetish" and live their miserable lives with this delusion.
Its the same reason why children that were raped often times turn into pedophiles themselves.
There are 2 ways that trauma can go. It gets resolved and you learn to accept the tragic event that happened to you or it goes unresolved and it has a profound impact on your lifestyle.
This goes hand in hand with the just world fallacy. The average person is so delusional when it comes to there being a just world that they simply can't understand that something negative happened to them because shits fucked yo.
Why do you mostly see dicklets, manlets, "gamers", weak men etc. go the cuckoldry route? Its simply because they are more likely to get cheated on in the first place, so its simply a numbers game.