NPCs will sometimes drop weapons when they are fighting or dying, or the weapon gets separated from them somehow, and then when they die the weapon becomes a separate object in the Skyrim game world. (Meaning, it's not part of the NPC's inventory if you search them, and must be taken/dropped/manipulated as a separate thing). If this happens, when the dead body is cleaned up the gear that got separated from its owner doesn't get cleaned up sometimes, and when you reload the game after that, the game has to put it back where you left it, and sometimes it glitches and puts it back in the same general location but it's off just enough that the stuff ends up floating or clipping into something else instead of being where it should be.
This is the only explanation I can think of for this phenomenon. I always found this floating stuff in locations where it would make sense that it was the debris left over from a fight where somebody died, the bodies have been handled by the game so they're not there but all the debris they dropped before dying is there. Sometimes I know this is the case, because I was IN the fight that left all the debris and wasn't able to loot it at the time, I'll go back along that same road and it's still there only floating at eye level.

In any case usually I've found that just walking into the stuff bumps it so that it drops to the ground. And if you are on PC the Unofficial Patch goes a long way towards fixing this problem IIRC by not allowing gear that is in the inventory of NPCs to be separated from them when they are killed, it remains part of their inventory unless you search them and take it. If you don't take it, it will disappear from the game world when the body does.