Convenience?   Sorry, but that's looking upon people who litter too kindly IMO.

People who litter are committing a deliberate act.   if they were that lazy why don't they drop things in their own car?  No, they want to be rid of the trash.  They deliberately leave it on the ground and expect it to blow away with the wind or they expect some minimum wage earner to pick it up.

These people should be confronted.   I've done it.  I've shamed people into picking up their trash that they've just dropped outside of their cars.

A parking lot may will never be as beautiful as a national park, but the attitude that it's acceptable to trash either of them starts off with deliberately dumping your trash.