It has been a combination of things - first, my wife has dated black guys since high school before meeting me at age 24 so it isn't new to her. I then was introduced to IR by knowing of her past, and acknowledging that she has a thing for black guys. Then in our relationship wanting to try new things we wanted to add a 3rd or 4th to the bedroom, but after trying to find another couple for a while it never worked out. We discussed another guy or girl at that point I said I'd be OK with another guy and she obviously preferred black guys, but that never happened either.
OK pause - then later on I found out she'd been cheating on me.... with all black guys. That led me to a realization.... she wants/needs more than I can provide. Kinda stimulated a bit of inferior/humiliation arousal in me somehow. Re-introduced it to our sex life as such, hotwife/cuckold and well, that's why/how for us.... Not really out of nowhere but happy to talk about it any time someone wants to know