If people pay for something, they feel entitled to take advantage of it. I've literally seen people fail to clean up after themselves and explain it as "that's what janitors are paid for".

Requiring a clean-up deposit up front will encourage people who were already inclined to clean up to do so, and encourage people disinclined to do so to leave trash behind.

The communal honor / shame culture that is in place is much more effective- people tend to care more about their reputation than they do money they've already spent.