I do not mind looting left over chests - just items to to sell for gold, and the chest location is marked on my map.
The other day, I looted a left over chest and got a gold lead!!! Definitely not complaining!
I think another factor is that auto loot is disabled by default for new players (it's been a while since I started out but I remember I had to turn it on manually). So it could be that many newbies are used to picky looting what they see as good value and leaving the rest.
Here is what is bound to be an unpopular idea, but would help. Just put a flag on players that would only allow for 1-2 open containers in the world, and if you left more in your wake, you would be unable to interact with any new containers until the previous ones despawned. Yes, there would be some kinks and rare issues to work out, but that would at least put the onus on the player engaging in the behavior.
I think another factor is that auto loot is disabled by default for new players (it's been a while since I started out but I remember I had to turn it on manually). So it could be that many newbies are used to picky looting what they see as good value and leaving the rest.
I've been playing since launch and I have yet to turn on auto-loot. I can loot pretty fast without it and it lets me see what I'm getting.