I try to think of that as being the same as irl: people never learn.

And also mooks are contractually genre-blind and never know how seriously they should take These Meddling Kids.

There's also the fact that it's Gotham, which makes it interesting because Gotham has more appearances at realism than some other corners of the DCU, so it would make sense that non-masked criminals would behave and expect much the same as they would in real life if faced with teenagers in capes.