Windwalkers aren't desired by higher end raiding guilds due to lack of effective raid utility while also being another Agi leather melee, thus sharing with Ferals and Rogues who offer more. Because of that, players, even those not even remotely at the level of those guilds, parrot that Monks are terrible.
You would also be surprised at how often I STILL see the argument of "leather tanks are trash. they take so much damage" when tanking LFR on my Brewmaster. I've had runs where a few people would try to vote kick me the moment a run started because "this run will suck without two plate tanks."