A. Actually yes there are quite a few special needs in the community, for example we have a lot of incontinent members. It kinda helps for these people to know there are others whom have the same problems they do, and that they can find communion and fellowship from as friends.
B. I see kinda what you mean, but mostly from those whom like to stick to the more crossdressing aspects.
C. That's also actually true, a lot of ABDL I know are very stressed and had quite a lot of issues in childhood that can greatly vary, and this just kinda helps them find some peace and security where they had none before.
D. Well everyone is something.
Psychology really can be quite strange, specially when it comes to the development of human traits. A lot of it though I think is influenced by media, such as seeing a character being forced into diapers in a cartoon for example, or an episode where everyone gets turned younger.
E. Again as stated with C, a lot of people do use them as a coping mechanism. Maybe a tough job, an unloving family, or just other problems with life in general. Sometimes it's nice for a lot of these people to just sit down and relax in a state of mind from when they didn't have responsibility, where they can relax and have fun being little again.
So I would say in a way yes a lot of that is true.
Of course there are also many other things as well, such as sexual interest, the general comfort of the garment compared to other types of underwear, and sometimes just simply things like "It's cute" or "I'm curious".