Let’s say you throw away something sticky, maybe a dirty diaper, or something else. You don’t want to get that stuff on your own trash can, and the garbage collectors don’t want to deal with soiled garbage bins either. It is simply about sanity, residues and stuff attracts rodents and other pests.
Both in apartment buildings and in houses with trash collection, the rule is that you put the trash in bags.
We generally don't have all that much super sticky trash. We also simply clean our bins when needed. Our organic waste bin, for example is simply lined with an unbleached kitchen paper towel that gets dumped into the container as well.
Not everyone lives in a big city. I'm not sure what I could put my garbage in to make their job easier other than some sort of bag. Find me a non-plastic bag that can fulfill this purpose and we'll have a reasonable solution. But since there is literally no other trash collection game in town, for now, the bags stay. I'll find other ways to reduce my plastic consumption, but I don't expect to fully eliminate it.
Part of the solution to that is to standardize it. Even outside of cities, the bins are the same and can be picked up by the trucks automatically. The only manual part is rolling it to and from the truck.
Of course, generally usingess plastic is always the better option.
I live rurally in the us, and don’t use trash bags at all. Our trash trucks pick up the bin and dump it into the truck rather than unloading in manually. I have noticed more roadside trash on trash days, because of unbagged trash.