While I know that there are A LOT of fakes out there. There are also a fairly large number of couples actively living the lifestyle on a daily basis. As jaggu008 said, most start as swingers. We did.
I think that the vast majority of real cuck/hotwife couples are empty nesters that now have free time and an empty house to explore the wild side that they suppressed for so long.
We started with a "by chance" encounter and turned that into swinging. I recently retired after a 28 year military career and during my deployments, I encouraged my wife to enjoy herself with others. After a time, that turned into us being more of a hotwife couple. After years of that, we started dabbling with cuckold arrangements. Since my retirement, we have experimented even further with the more hardcore aspects of cuckolding. I am not sure if all of it is for me, but it is fun to experiment.
Great topic.