Adult diapers are quite a bit different than baby diapers, also. Just making a baby diaper in adult sizes would not work, as adults are proportioned differently.
I think this is a myth that is often mentioned when this subject comes up.
If an adult diaper were designed like a baby diaper with the only difference being that it was proportioned for adults, why wouldn't it work just as well as it does on babies? A single tape on each side would have to be a little wider in order to fasten and hold the diaper on securely, but the actual sides of the diaper would start higher and taper up along the outer thigh, resulting in a look and fit just like a baby diaper. If you open up a baby diaper and lay it flat, it's proportionally wider in the center, where the sides or "wings" are only slightly wider. A typical adult diaper is proportionally narrower in the center, so the sides extend out farther. Think of how much easier this diaper would be to put on and take off. It would facilitate wearing much more often, particularly when it wasn't practical to actually use it for wetting until a later time.
About ten years ago, I read of one such one-tape-per-side diaper for adults, somewhere in Japan, but could never actually find some for real.
Also, among cloth diapers, there are places where the adult version of them is pretty much the same as a baby diaper, only bigger. So, I don't see why that wouldn't work for disposable diapers as well. The limiting factor would seem to be the cost of setting up to manufacture a relatively smaller volume of adult disposables (unfortunately) that probably wouldn't sell in numbers large enough to make a profit, even as many AB/DLs would buy lots of them.
So a petition would be a pretty ineffective way of going about this. If there's a market for it, someone could just build it, and people who are interested will come. Easier to say than do though...