Gear oil is designed to protect gears from wear. In a scooter situation, it's protecting the gears in the final drive..
This must be more of an issue than I thought. When I checked the final drive on my People 50 (well used when I got it) there was pinkish fluid in there, which immediately told me there was AFT in the final drive.
I think the last motorcycles that actually used ATF were the early 80's Hondamatics that actually used a automatic transmission, not a CVT.
That said, I use ATF in the forks of several of my motorcycles when changing fork "oil".. I like it because ATF Type F is 7.5 weight. Fork oils come in 5, 10, etc.. I find 10w too heavy and 5 too light. While it's not taboo to mix fork oils to get the desired viscosity, I just go with ATF Type F and instantly get 7.5w.
The reason it's allowed with this situation is because forks aren't gears. It's all about forcing fluid through orifices and weight and viscosity is what's desired, not wear protection.
Just something to remember when changing fork oil someday.