Can someone explain cucking to me?

How is this a real fetish? How broken does one have to be to want others to fuck their wife. Does it come from a place of self hate? I don't understand.

Why is cuckold a fetish? I cannot think of anything worse.

This video sums it up fairly nicely, OP.

https://www.youtube.com/watch?v=SE6jy78tV78