The four strokes are selling based on their fuel economy and
emissions, not on performance

Also because of the smooth power curve. I said real early in this thread that
if you are a go fast guy you need a 2 stroke, for lots of reasons. 4 strokes
make more sense for guys who go slow to medium speed (3000-4000RPM) a lot with
occasional WOT.
At WOT or close, it makes a lot of sense to have fewer moving parts.