You are right, they should simply have a mana bar, health bar, give infinite pots, and allow people to hack and slash through to easy victories, you know... because people will cheat it anyway. Tardsole on brother!
It's preferable to make-work.
One of the first solutions to the problem of too much loot I encountered in video games, was a spell that could turn loot into gold. Sooo... Instead of having to run back to town every 5 mins, you had to spend pretty much the same amount of time fiddling with your inventory and resting to regain mana. In other words, it was - and remains a popular - non-solution to a "too much of a good thing" sort of problem.
Crafting & durability in CRPGs tends to present the same type of problem, and when it gets addressed, it tends to be addressed in similarly absurd ways. And I know I'm saying "tends" here, but I can't actually think of an exception in CRPGs.
If durability is meaningful in a combat encounter, then it becomes a problem akin to Vancian magic: if you have a high frequency of combat encounters, durability ends up being a mindless chore just like resting for 8 hours every 20 mins of in-game time, in places no sane person would rest - and if it requires special resources then you're essentially forcing the player to go grind every so often.
Crafting is much the same. If it's to be meaningful and not come across like a bullet through the 4th wall, then it has to work pretty much like producing stuff in the setting works in general. Typically that means tracking down the right sort of tools and raw materials, the right kind of expertise, and then paying for all of it and waiting until it's done. So again; a Vancian magic sort of problem that ultimately boils down to make-work.
It's asking the player to spend time in the game without playing the game. Or if you prefer: tardsole'ification - in practise making the player waste time clicking pretty little GUI buttons for the sake of clicking them is no fucking different from replacing systems-based gameplay with QTE-ridden cutscenes. The end result in both cases is making the player behave like an automaton.
Obviously both durability and crafting can work really-really well with RPGs. As can Vancian magic. But not if it's Infinity Engine-like CRPGs. Those types of games have far-far too much combat for durability to not either be meaningless or really fucking annoying, and they have far-far too little narrative and much-much too tight narrative structure for crafting to be anything other than utter fucking nonsense.
- I mean, I'd love to be proven wrong (and I'm guessing that's slightly more unlikely than someone proving the existence of divinity). But I'd love it even more if they just didn't bother and spent the time and energy on the shit that's actually fun in IE-likes.