Multi-select is like communism: it's a good idea, but it doesn't work. I mean, how many CRPGs have multi-select in inventory? Off the top of my head, I can't recall any (BG1 / 2 had multi-select in the shopping interface, but not in the inventory per se).
Original Sin 2 has multi-select, but only for the controller-UI and mappings. People who come from that experience tend to wish it was there for keyboard also. Why not?
The key word here, I think, is "controller". It has many more buttons than any mouse, and most of them have 2 joysticks, which expands the possibilities a lot.
I mean, I don't blame Larian if they are unwilling or unable to come up with a sensible kb+mouse multiselect. I've never seen a single good implementation of it in my entire life, probably. I suspect there aren't any around, otherwise the approach would have been copied by everyone else very quickly.
The thing that bovvers me the most is the right-click menu in the inventory. It's too academically implemented, and as such it's too cumbersome to use, esp. if I need to send 15-20 food items to camp (because, as of now, camp is the only place where I actually need food, and pig heads tend to weigh quite a bit).
There's more than one way to skin a cat, of course. A not-so-unreasonable approach would be to drastically cut down the amount of available loot (say, 20-50 times). This way, everything we find becomes "special", and it's not a problem to deal with a couple of items (literally, 2-5, no more) after a full run between 2 long rests. There are many approaches, Larian just needs to choose one of them, but as of now, they don't seem to be particularly concerned with the issue.
