They don't know to put an item back where they found it? No. They're just lazy.
Yes, they are lazy, and it makes me mad when people just drop stuff. Just like it makes me mad when they leave their shopping carts in the parking lot so you can’t get into the space, rather than take the carts to the cart drop-off area. Things like that are annoying.
But they’re not stealing. The stores really need to have employees keep things tidy and also perhaps start a campaign telling people what to do with items if they change their minds, etc. They also need to have enough people on the registers or enough self-checkout stations that people don’t get frustrated waiting to buy something and just dump it and walk out (which I have seen often). I think creating a good atmosphere (clean, neat, etc.) helps a lot in making people behave better, and that’s something that can only be done by the stores and the managers themselves.