Why can't people just throw stuff away?

I hate when people liter, I pick up a lot of other peoples trash but OP's picture has overflowing trash carts. Clearly the venue didn't provide enough trash containers. I would have held my trash until I found a not overflowing container, but most people won't.

I live in London and cannot fathom how incredibly apathetic people are here about littering. The whole city has it everywhere. No one cares. They fling shit away the moment they’re done with it. But how can you make people care?

So many just don't care. They'll say its just not my responsibility or who cares someone will pick it up anyway.