Issue is, gymbros are the worst gatekeepers. They either think they can turn everyone into a top atlete by demanding everyone to act like one, or want to "keep it a niche".

Yes, a lot of counterexamples exist. So are a lot of counterexamples to techbros, toxic gamers, etc., but when people talk about toxicity within these circles, they're not talking about the good ones, and even "gradual toxicity" also do exist sometimes.