Why arent any people trying brushed motors…what are their disadvantages for efoiling…for examlpe
http://www.hydrogenappliances.com/1hp_motor.html
I think for the same reason why we do not use horses any more 
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The best efoils with optimized front wing and propellers can fly at 800-1000W. However, to reach the takeoff speed and get on plane, you need a kick and five times this power. That is why our efoils motors are in the 4-6kw range.
Then, there is this 2018 answer 
from @MaB
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… which I can confirm. Pack 4KW max power, 1.5KW in S1 duty service (continuous) into a 60mm tube ain’t a joke. Brushed motors are NOT maintenance free nor efficient.