Dashboards are not bolted directly to engines. The issue is that motorcycle parts are more directly connected to the engine. Sportbikes normally use the engine as a structural member, bolting all the other bits and pieces to the engine block. So vibrations through motorcycle handlebars and such are more intense than those on the dash of even an extreme muscle car.

Ignore the motorcycle bit completely and just think physics

You could trigger this on any oscillating “body” if that body is oscillating at a certain frequency and amplitude combination.

It just so happens motorcycle engines produce that combination. There would certainly be others. tHe sustained nature of the shaking would also be cause for concern but I didn’t see any mention of duration in the support article

Potentially? But it’s a known issue only to motorcyclists and (pedal)cyclists. idk why Apple is saying this is due to engine vibration but I think it has more to do with hard suspensions.

No

Source: personal experience