I would think it has something to do with the C.P.S.C. being involved in quad sales, and not snowmobile sales.

 

While product liability has a lot to do with it, so does usage.

ATVs, especially utilities, are analogous to Jeeps.

A high-revving, high power engine is of less use than a lower-revving engine with a lot of torque - preferably at lower RPM. You don't see a lot of non-diesel turbos or superchargers in offroad vehicles.

Not to mention the challenges of effectively putting that power to use in a 4WD system. Add locking differentials, etc... and that high-powered engines seems a lot less useful.

Now, perhaps some of the sport quads could use high-revving, high-powered engines, but they seem plenty fast they way they are,