People are talking about social graces, and you want to take the
cynic's viewpoint.
Now you want the bus companies to deploy more buses, and to hell
with asking passengers to move in.
How about this: ask passengers to move in and be less selfish to
those who want to board on top of getting the bus companies to
increase frequency?
And answer my question: would it really kill you to give up 30
seconds of your time to clear your tray? And would having one less
task to do really make the McDonalds' auntie lose her job?
If you're lazy, just admit it, and stop trying to justify your
stand with these ridiculously cynical excuses. 
Think about this. You are the manager of MacDonalds
Restaurant.
In the past, noone clears the tables, you have to hire 2 cleaners
to clean the tables.
Now, everybody clears the tables, what do you do with these 2
cleaners?