Same reason you don’t leave oily rags, fuel soaked trash etc in a garbage can in your garage. Spontaneous combustion.
Decomposing trash creates heat, noxious gases, methane, etc. If everyone did what you say you do, there would be more fires than they already have. There’s a reason it’s illegal. Maybe a little less pompous sanctimony and a little more respect for the people that have to clean up your crap. Do it right.