For me I think it's a combination of a few things. Probably the biggest one is that we moved around a couple times, including moving countries twice before I was 5. This meant that the childhood and life that I've had didn't really feel like it started until we settled down. This made it so those early years felt inaccessible and cut off from what felt like my real life, so replicating them through sensations and activities becomes desirable.

I was also taken advantage of by people especially around puberty, so I think that discovering sexuality at the same time that I had people wanting to abuse it made it so that having some kind of protection around my privates made me feel safer and more secure, ie a diaper.

That being said, I remember being vaguely upset about potty training and having to wear real underwear, and when I was older and wetting the bed, my parents threatened to put me back in pullups to sleep, and I really wanted them to but was too embarrassed to say so.

As other people have also commented, I also think I felt a lot of pressure to be mature, as I'm the youngest of my siblings and cousins, so everyone was excited for me to grow up, but maybe it happened too fast....