What's the psychology behind men that enjoy Mommy Dom Little Boy)?

Wellll, it depends on who you ask, because that's hasn't been much research into that specific kink. None, afaik, but I'm hedging my bets.

What has been researched is general role play in a sexual context.

So, you're going to run across what amounts to pet theories and outright speculation when specifying that kink.

Now, my personal pet speculation is that it likely starts with an unbalanced mother figure at some point and then develops into a kink due to unresolved conflicts arising from that during puberty.

If you look into what little research has been done into fantasy and role play, you start seeing patterns. Psychology has a reproduction problem, but you can still make use of one-off studies, if you're willing to go digging for them, and don't mind dealing with the stuff that's published as books rather than a formal and well organized publication.

One of those patterns is that most kink, paraphilias, form very early on. There seems to be a set of circumstances that makes the formation of a kink more likely. There needs to be a "rush" of some kind, there needs to be a form of sexual or sexualized element to the triggering event/s, and very often it needs to be during the early stages of puberty, or soon before.

So, you can see that, assuming that is accurate, you have the potential for a lot of parental or familial related kinks.

In this specific question, let's form an imaginary origin story for entertainment's sake.

Little Bobby is becoming a big boy. He has discovered his pee-pee feels good sometimes, and has noticed that big girls and little girls look different. He's got the beginnings of sexual feelings, but they are still vague enough that he isn't thinking in terms of putting his penis inside another person.

Little Bobby gets bent over mommy's knee for being a bad boy. He gets spanked. His peepee is pressed against mommy's leg, and as she spanks him it feels good, despite the spanking feeling bad.

Bobby loves his mommy. She doesn't spank Bobby so often or so hard that it creates a high degree of trauma response, but it does register as a trauma that needs resolution.

Bobby has a cocktail of semi-sexual sensations mixed with some fear, some anger, love for his mother, and the sensations of being a "bad boy".

While grossly over simplified, and pinned together purely as a thought experiment rather than a true representation of reality, you can see that Bobby hitting puberty with those memories is going to set him up with a proclivity to receiving extra stimulation when more of those factors are together. Since we very often get "attached" to the circumstances surrounding our earliest sexual experiences, if Bobby amplifies his enjoyable sensations while remembering those events, you have a recipe for kink.

It isn't that Bobby wants to fuck his actual mother, though there are people that do. It isn't that Bobby wants his actual mother to be involved at all.

Bobby simply has a strong sexual link to a set of stimuli that are best created by putting himself back in those formative states of mind. Humiliation, fear, anger, the physical sensations, they all combine to be greater than the sum of their parts. Bobby may enjoy being a submissive in other play, but when it's mommy/boy play, it's the strongest because it's closest to the most primal origins.

It doesn't have to say anything about the person, other than them having had an atypically potent event that linked non sexual situations to a sexual feeling.

One example from Nancy Friday's books about sexual fantasy formation, a guy had a fetish that combined voyeurism, panties, and legs.

The man had been allowed to play in a changing room at a fancy event. Iirc, he specified a wedding. But he was young enough to just sit under a table playing with toys, but old enough to have a pre-sexual interest in women's bodies.

The sense of being separate from the women changing into fancy dresses, and shoes, while walking around in underwear in a way that was unusual (women weren't prone to taking pew walking around in undies normally in his life), along with the excited atmosphere made the event more stimulating.

When he later began sexually fantasizing, the memory of actual women in their underwear was the most real memot he could access. Fantasies have to form from something. If you are interested in having sex with a woman, you'll have to form imagery out of what you have already seen, and mix it with what you think it's actually like.

So, this guy starts spanking the monkey up a memory of women in their underwear, not seeing him, forgetting he was even there, and the enhanced pleasure of masturbation converted it to a sexual fantasy that became a strong kink for him. His most enjoyed fantasies as an adult were of hiding in changing rooms, watching women change clothes.

That's a very linear example, but I think it informs the general process of fantasy and fetish formation rather well, as a single example that was presented as being from an actual person. Nancy Friday was pretty well respected in her field, so there's no reason to assume she made anything up.

There's also the aspect that, as adults, we very often feel stressed and unable to escape our lives. Role play of any kind helps with that. When the role play takes us back to childhood, even better. When it involves not having any responsibilities, having someone take care of us, you get another layer of relief. When it's also sexual, you top that role play cake with some nice ganache icing that makes it possible for people to become so reliant on it that they're unable to experience sexual satisfaction without it. I becomes more of a psychological problem sometimes, because it becomes disordered.

See, kink isn't disordered. It's a fairly normal thing to have non sexual things become part of sexual enjoyment. Candles, lingerie, feather boas, they aren't sexual in and of themselves, but plenty of people find fucking by candlelight "special" somehow. It only becomes disordered when you can't function sexually without it, or the desire for it interferes with the rest of life.

Which brings us full circle. The psychology behind it isn't clear in specific. We can only infer from other partially understood phenomena what is probably behind it. And, even if someone pops in and explains their kink, it's still only one example, and can't be used as definitive. You'd need a much bigger sample that included personal histories at the very least. Even a very self aware individual will likely have biases towards what they want their psychological state to be, what they want their kinks to mean, so it takes a lot more samples to make sure that patterns exist, and to have enough background to guess what the causes may be

Based in my limited understanding of psychology, it's about role reversal. Meaning, they are in a position which gives them quite a bit of control in their day-to-day life. This is why in the show Billions, the DA of NYC is into BDSM. He has a level of control over others that's quite immense. This over time leads to him enjoying being taken advantage of in the bedroom. But again, I've only studied a limited amount of psychology, and the rationale behind each person's choice to be dominated will have some variation, as it's psychological. But this is the general idea behind the Dom/Sub preference.

Escapism and release.