Just for the sake of discussion;
thumb throttles showed up early on snowmobiles maybe because they can be operated easily with heavy winter gloves or mitts. But they do not allow the thumb to wrap on the grip like a twist grip does.
Twist throttles allow for a full hand wrap around the handle bars. One can get a better hold on the bars than with the thumb throttle grip. They can be operated with insulated gloves but with much less finesse on the throttle. Motorcycles are usually operated in temps above freezing so wearing thin gloves or none at all is not a serious problem.
So throttle grips on snowmobiles in the winter and twist grips on motorcycles in the summer makes sense to me.
But what to put on quads ? The four season capability might dictate a thumb throttle. Chances are either thumb throttle or twist throttle could work well on an atv depending on how, when and where it is used. Maybe.