Yeah that's not it chief. And thinking "non-normies" are all basement dwellers with no [social life] is extreme normie reasoning.
In this case, you call people normies because they stumble onto something they don't understand and don't appeal to them, and their instinctive reaction is to shout "but why" with various degrees of obnoxiousness. Granted, you're allowed to be curious about stuff, but a) you're not the only one with this kind of behaviour so don't take it too personally and b) most of these "outsiders" tend to insult people with zero self-awareness. The normie part comes in because it makes one wonder if any of these people are into anything but penis into vagina in missionary position with the TV still turned on for some reason, aka regular basic vanilla sex. Fact is, anyone I know with a fetish they have no issue having tend not to really care about other people's fetishes, even if they can't begin to comprehend what's hot about it. Reason is they are usually able to relate to these people because they themselves are into some kind of obscure fetish, which other people might not understand. And so empathy takes it away; you're not into it, it's not your thing, you move on. What fetish isn't weird anyway.
This phenomenon is sort of exacerbated when it comes to the "AB/DL" scene, since it's both obscure and terribly misunderstood. The association with pedophilia is very common, but also extremely ridiculous. I suppose medically incontinent people are not allowed to have any kind of romantic affiliation during their entire life; they do have to wear diapers all the time.
I should also point out that, like with everything else that exists, it is a little pointless to try and cast a net over something and try to come up with a general explanation that will fit everyone it concerns. This is a sex thing. It's not something that works the exact same way for everyone. But let's give it a go anyway, from the weird part to the weirder part.
The "diaper lover" part: pretty self-explanatory. This is about the diapers as clothing items. Either the look, the feel, the usage of it, that's what matters.
The "adult baby" part: which involves roleplay, and will make people shriek most of the time. It's generally about regression, "refusing" to be an adult and be considered much younger. Despite the "baby" part, not everyone wants to be considered like a literal baby. For some people, it will simply mean submitting to another person's authority, without pretending to be younger than they actually are.
Those terms are grouped together because it's common for people to be part of both, but that's not always the case. In fact, there's yet another "fetish scene" referred to as "DDLG", which is very close to the "adult baby" fetish but without any reference to diapers.
So what's the part that turns people on? Well, once more, it will depend on the person, but it's usually about:
Humiliation: pretty simple, this is more about the "punishment" side. Forced into diapers, forced regression, BDSM, all that jazz. Big on the dominant/submissive relationship, obviously.
"Comfort": actually not sure what word is the "official" one. It's the opposite of the humiliation, with the same dominant/submissive relationship, although the "dominant" is considered a "caretaker". Although sometimes punishment and comfort overlap. This is also the side that people who are into it but "in a not sexual way" are attracted to, but I'm hardly qualified to talk about that.
Clothing: the DL part, or anything that are somewhat associated to diapers, like onesies, or pacifiers. You can simply like the accessories for what they are.
Omorashi/Scat: because, as surprising as it may be, those don't really "do it" for everyone, wether they are AB or DL or both. Omorashi is admittedly common, but scat is where a lot of people draw the line. This is more about two fetishes overlapping, as people who are into scat are not necessarily into diapers and vice-versa.
So, voilà. For the average person, what makes it work will be a mix of all the above, with different levels of preference for each side (going from "very high" to "zero"). And also some stuff I don't even know about, probably. Ultimately, it is pointless to try and find an archetype that works for everyone, or even a majority of people. Which is also why it's a little pointless to ask "but why", since the answer will be different every time. Just leave fetishes where they are and concern yourself with what works for you, I guess.
