The driver isn't a gatekeeper or tollbooth collector. They stop, you pay your fare. You don't pay the fare they aren't going to argue with you, just pull off to the next stop. Because the bus driver has a schedule to keep and if he has to stop the bus for every minor infraction (and eating on the bus is very far down that list) than the schedule becomes unreliable, people stop taking the bus, and then revenue drops.

And all of this could have been avoided with a trashcan on the bus.

If you've watched anything on youtube you'll see that people escalate a situation for some of the stupidest things. The world is full of crazy people and they drive or take the bus too.