>>103603 (OP)
From my brief research in addition to my own story, the genesis of an individual's ABDL fetish is inconclusive. Most researchers site that due to the fetish being clandestine in nature, it's difficult for them to capture enough data to derive a conclusive answer. Although the ones that did survey smaller sample sizes had admittedly speculative answers.
I recently found that my ABDL fetish came to fruition due to my childhood. More specifically, a lack of childhood - I had well-meaning parents that eventually divorced but one was an over-bearing, passive aggressive, overly sensitive helicopter parent while the other was distant, verbally abusive, arrogant, impulsive, financially irresponsible and a raging drunk.
Thus, most of my childhood was spent existing in the valley of dichotomy between my two very different parents, i.e. trying to escape the passive aggressive, highly sensitive, over-the-shoulder shadow cast by one parent by spending more time with the detached, irresponsible, arrogant drunken parent only to endure the fallout from the former later on which was then followed by drunken irresponsible episodes from the latter, leaving me sandwiched in-between with no side being favorable for me to join.
All that to say, in summary my fetish is the result of what I consider to be premature stress (or experiencing consistent levels of stress at an immature age to properly manage it) in addition to a reaction to the power dynamic my parents relationship consistently forced on me.
I, like many others here, became interested in ABDL at a really young age. Although the research has yet to conclude anything empirically, some theorize that the fetish forms at a young age during which sexual imprinting is taking place, but an absence of female/male genitals is replaced with an association to whatever is proximally closest visually or by olfactory. This also applies to other fetishes as well.
I think many of us like to think there should be a prevailing causation for the ABDL fetish among the community, but I tend to think that due to most fetishes having multiple dynamics (ABDL can be AB or DL, or both while also being more preferential towards role play, BDSM, etc) that there's likely a multitude of causations that are all correct answers.
For myself, I enjoy the roleplay dynamic with my wife playing either role. When I'm the one being diapered, it fulfills my desire for stress reduction while also stimulating sexual arousal from the sensual experience of the diaper and the power dynamic she leverages as the dominant. In contrast, when she's the sub, it stimulates my sexual arousal from the same sensual experience but from the opposite perspective while also being in a position to be domineering to her.
All of that, in my opinion, speaks back to one of the three variables of my upbringing; premature stress, parental power-dynamic, or misappropriated sexual imprinting.
Below are links to information I've read previously in my own search for my own fetish genesis.
https://www.routledge.com/Variant-Sexuality-Routledge-Revivals-Research-and-Theory/Wilson/p/book/9780415729895
https://medcraveonline.com/MOJAMT/the-use-of-cognitive-behavioural-therapy-on-two-case-reports-of-paraphilic-infantilism-substance-misuse-and-childhood-abuse.html
https://books.google.com/books?id=5bAPxqDyFxUC&pg=PA530#v=onepage&q&f=false
https://pubmed.ncbi.nlm.nih.gov/29525580/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7068517/
And, of course, can't forget about Wikipedia
https://en.wikipedia.org/wiki/Paraphilic_infantilism#cite_note-Cantor-16