That is indeed a curious mechanic

Maybe also having more consumables in the world and less fitting in your inventory would be a good thing? So that the player feels they'll just waste it if they don't use it, and it's not that rare anyway.

I like that. Anti-hoarding mechanics, I guess. I can't remember which game it was, but one I played recently recharged your mana/energy/mojo or whatever between fights, so you were encouraged to actually use the abilities instead of tediously avoiding it for most of the game. "How do I best use the total available mana for each battle" is a bit more fun than "Better pretend I don't have these abilities most of the time."

This is similar to why I actually came to like the rapidly breaking weapons in the Switch Zelda games. Once my mindset became "don't bother hoarding good weapons, just use whatever you want because you'll just find new ones all the time" it stopped being annoying and instead kept things fresh.

That's the reason that consumables and money don't carry over between levels in Thief: The Dark Project. No point in hoarding stuff, you might as well use it. Except of course that if you're good, you don't need to use any items at all - not even the blackjack.