So I started checking other areas where I was having issues and discovered similar situations in most of them. They were battlegrounds that where constantly active that I passed by frequently without collecting drops.
At first it's no problem, but after 20, 30, 40 levels of accumulation it becomes a significant burden. At lvl 95 it's grown to be a problem nearly everywhere from settlements to inner city blocks.
Cleaning up after everyone in the commonwealth is growing tiresome. I don't know what the cap is on weapon drops from fallen enemies, or the fade time for trash. But whatever it is, it needs some serious tweaking. I have no use for 90% of the crap dropped by enemies, and looting weapons just to dump them in a container is ridiculous and annoying.