I don't know the answer but I would think another element to consider is the increasingly litigation conscious world we live in and the possibility that some numpty will stick the maximum rated engine on their boat and then sue somebody because it chine walks at full moo, chucks them out and then runs them over because they didn't bother with the kill cord because it was "only in the bay and it's calm". So to reduce the liability, reduce the HP and you will reduce the idiot factor.
My old Humber Destroyer was rated to 150hp on the plate but I think the same boat made now is only rated to about 130.
A Boat is a hole in the water, surrounded by fibreglass, into which you throw money...
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