It simply says they can use the feature that often. It never says that it’s an at-will action/feature. “At-will” isn’t even a game term in 5e as far as I’m aware.
Or it replaces it with an even more complex inventory tracking game of how can I fit all of this in a 4x4x4 feet space. I’m sure some mathematicians would have a field day.
Yeah, that is so frustrating as somebody who plays a character that requires short rests. Our sorcerer throws out her 5th level spells every encounter and I have 2 spell slots as a warlock…