I think what drives us to ABDL if highly individual, I myself had no trauma potty training or abuse as a child (aside from the odd bullying in school from other children mostly because I was a bit of a geek). I was also potty trained not early but not late either and had no troubles with bedwetting (aside from after I began to get these feelings and started doing it on purpose).
I mentioned before but I think the tipping point for me was at about 7 when I had an accident at the park visiting my dad, it was a one off and hadn't happened for many years and didn't happen again for many more years, but my dad kinda lost it a bit and drove me home to mum and put a nappy on me demanding she keep me in them for the rest of the weekend before storming out. This was absolutely humiliating for me at the time but was the first real exposure I had to wearing nappies outside of infancy.
My sister at the time was not even a year old so there were still nappies around the house, while I hated this event at the time within the next year is when I started being attracted to them, wanting to wear them and wetting my pants/bed on purpose.
So for me, yes the ABDL desires probably were triggered by that trauma but it was later on in childhood.
For others it probably depends a lot on how they were treated at various ages, what they were exposed to, their own personal emotional state and many other things, there is no one contributing factor that will guarantee someone becoming ABDL and what may be the cause for one person may also be what stops the desires from starting in another.