I think there may be more than a simple fetish involved. Adult diapers and other incontinence products are much more in the public eye than they used to be.
Before June Allyson did commercials for "Depends", adult incontinence was not discussed in polite company and what few products were available were hidden in a dark corner of a drug store or "surgical supply" store. Now many stores openly display Adult diapers, pads etc. and sell a BUNCH of them.
There are commercials on TV, ads in magazines, and many comedians refer to adult diapers as part of their act, etc.. Advertising used to be aimed almost exclusively at the elderly. Newer ads are more inclusive of different age groups.
There is definitely a fetish side to it too, but I think that adult diapers are being worn by a lot of folks simply for practical reasons.
They may not be obvious about it, but college students may wear "protection" during long tests. People making long flights or road trips may elect to wear to minimize "pit stops" in public rest rooms. Other people wear for convenience during extended shopping or even at work. Since they have to urinate often, pregnant women often wear pads or pullups especially during the later stages of pregnancy.
As a DL, I think it's a good thing.