They do. The smokers don't care.
And even there was no ashtray, that's still no reason to dump trash on someone else's lawn. Employees don't throw their lunch wrappers on the lawn when there's no trashcan.
So every single one of the smokers doesn't use the ashtray?
That's about as believable as your assertion that not a single employee ever tosses his food wrapper on the ground.
I've seen more McDonald's wrappers lying around than just about any other garbage.
On your argument, everyone who eats McDonalds dumps their wrappers on the ground.
Did your company (or you, for that matter) ever try to identify which smokers are butting out on the lawn? Or are you just assuming that they all do it, in the same way I just assumed that all McDonalds eaters are litterers?
Blaming everyone for the actions of a few is called scapegoating, and should have no place in your argument.
I won't even get into the philosophical problems I have with non-smokers kicking smokers outside (away from their ashtrays) and still finding fault with them.