Yep, it sounds like a way to "punish" pax without having to resort to fines (the negative PR from which would really be incredible to see), and without the blatant retaliatory secondary.

It's really passive-aggression at its worst. "HAH! You're going to miss your flight if you don't toss that in the trash, because you'll have to go back to the end of the line to put it in a baggie if you don't!"