Same here. They may think we are not smart enough to divide the stuff properly, and that there may be some useful/valuable stuff in the bags, LOL.
The cat litter cannot fill a whole bag or it will break apart -I double bag and it is still really heavy. So the empty space is used by other people, usually market vendors, to stuff their stuff. I do not mind, I am not using the space anyways and usually they insist on throwing out the garbage themselves. Plus, it gets me on their good side, which is good when buying stuff from them or, as it happened, when I was sick they helped me out with chores. Even came to my house to pick up the recyclables or help me buy stuff from 711 when I couldn't even walk there. I strongly advise to keep in good terms with the neighbors, folks.