The Ninja is a 4 stroke twin I don’t know about the others though. So EPA shouldn’t be the problem. IMHO it reflects the market place. I don’t think many people in my MSF class even considered a 250cc as a first bike apart from me. There was a lot of discussion from the class and teachers about the 500-750cc cruiser bikes.
Now I would have thought with the sales of the Ninja that the other companies would have noticed and figured they should try to compete for those dollars. Maybe there needs to be a push from dealers to get Honda, Suzuki and Yamaha to import the small cc sportbike models they sell overseas.