I think there are several factors, like smaller international fandom and not accessable to the world. But even that, the most important thing is the japanese and their culture itself. Japanese are more timid, reserved and avoid dramas at all cost. That's why you barely see japanese fighting with each other. At least not in public so much. Whenever I see some glimpse of toxicity of Jpop fans, it's mostly on youtube and these Jpop vs Kpop videos.