I assume it has something to do with junction capacitance. Since I need big diodes for my 25 amp stall current I want to use plain old bridge rectifier modules. Big and fast diodes are expensive.
Big bridges are cheap and easy to find.
It also seems to me that my diodes don't have to be as large as my supplied current. They only have to conduct for a few microseconds. But I can't reason out how much current it will be.