Because they think that someone is being paid to pick it up, so why should they (a) do their job for them and (b) do it without being paid.
I guess it's a variation on the old upper-crust belief that the nobs are pretty much obliged to throw their clothes on the floor because "that's what the servants are for".
Times article claim that Waspi women are tone deaf and should read the room
Husband wants us to go to live in Portugal
