system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does garbage have a distinct smell when it's such a large variety of waste items?
gpt
You're not smelling the garbage. You're smelling the stuff given off by the stuff that feeds on the garbage. Most food, whether raw or cooked, generally isn't that smelly (yes there are exceptions). But after a while in the garbage, that food starts hosting a lot of bacteria and fungi and molds and other stuff that give off a lot of waste gas as they break down that food's tissues. You'll really notice it with, say, uncooked meat juices such as when you toss out the packaging on the Big Box Store box of chicken legs.

We humans are pretty good at picking up rotten-food smells because knowing food is off and not eating it was a critically important skill for survival. For this reason, to us rotten food smells overwhelm the weaker smells of the constituent foods in that bag of garbage, and the liquids that are full of them can leak out and be absorbed into stains in the container or dumpster walls over time so they really stick around.