By the time you've gotten 500 commendations, you've probably gotten into the habit of being kind and courteous in instances (or at least gotten into the habit of NOT being a total asshat). Certainly there will be exceptions, but by and large I'd guess the player is rare who, after dinging that 500th commendation, sez to themself, "Well, dang, no more rewards to get - time to unleash my inner troll lolololololol!"

I wouldn't turn up my nose at further commendation rewards, but I don't really see any need for them.