There are like a billion crates, barrels and other containers, and you have to check ALL of them, if you don't want to miss the few items that are really useful.
Not really. Crates and Bookshelves are the only worthwhile containers to actually bother looting. Since these can contain Thieves Tools/Disarm Kits and Scrolls respectively.
Barrels, bottle racks, vases, pots, don't contain anything particularly useful (Barrels can also contain tools and kits, but at a much lower rate to the point where it's just not worth the time to check)
Even then, by Act 2 you likely have like 70+ Thieves Tools and 50+ Disarm Kits and 20k+ gold to simply buy more from vendors if somehow you use them all.
To make matters worse, the UI does not consistently highlight every relevant container type. An empty pouch is highlighted while a skeleton that may have an awesome ring is not. This will result in spending a lot of time carefully investigating every area, and probably still missing a few great items
The very few scenarios where this is actually relevant are all scripted. So after 1-2 playthroughs you should simply know the skeletons that contain actual loot and not just some random dagger or bone.
This is made worse by the very linear nature of the game, since you can't go back to earlier areas to get the stuff you have missed the first time.
Umm... You literally can.
Until Act 3 anyway. But if you're entering Act 3 you're going to the area that contains all the stuff that completely invalidates all the junk items you'd find from the prior 2 acts by having a plethora of vendors selling the highest tier stuff.
Why so many hyper-niche equipment items?
There's really not that many. There's like 2 items with Drunk synergy, 1 item with small race synergy, 1 item with Drow synergy, 1 item with Dwarf synergy and then a handful of build dependent items.
The bigger problem is there's just so many bad or underwhelming items. Runs often end up all boiling down to the same handful of actually good items every time (Things like Knife of the Undermountain King, Phalar Aluve, the single cloak that gives +1 AC, Melf's First Staff, Caustic Band, Ring of Protection etc).
Which is made worse by the fact that all these items come from scripted sources. Mostly vendors but also static locations.
There's no finding random magic items in containers or on enemies to make looting spicier (Or pickpocketing worthwhile), it's all just "Go to X location and pick up Y item and move on". It's why pushing enemies into chasms doesn't feel bad, since you know you're not missing any loot because you know 100% what every enemy drops.
