It's the principle of manners. You should clean up after yourself. Service crews are there to clean up the mess from eating (spilled juice, food remnants, mop the floors etc). The garbages are in a public place for a reason - to be used by the public.

This kind of attitude would be going to the toilet at McDonalds and pissing all over the wall...meh, they have mops...and they're getting paid to clean the restroom anyways, I might as well LET ER FLY!