Just because a cosplayer is a professional doesn't mean that they're allowed to bring their costumes wherever they go.
Their hard work got and credited them.
Depending on the character, it may very well be the case that there are plenty of kids around.
The promotion goes both ways and it's a courtesy to reference someone else's work, especially if it's bring worn by a professional cosplayer.
It should go without saying that those participating in the same craft should respect others who are doing the same.
If there are no outside food or drinks, cosplayers must follow that rule.