Bingo. It's finite resources in a game with a relatively fixed duration that make those ideas compelling. Do you spend your hard-earned money repairing your gun or buying a new one? Do you get health or ammo? If you go out for a long trek into the wilderness, will you have enough to make it back alive? Meanwhile in a Bethesda game you are rolling in supplies all the time, money is infinite, you can just steal high-value stuff from NPCs (which often respawns after a few days), kill some bandits to get some cash or items to repair with, etc. Those games are built around exploration and character progression, not resource management, because for the most part the resources you are concerned with are transitory. The "real" things in the game you need to acquire are your XP/skills and map markers.
But that's just bullshit.
Resource management can occur and have different dynamics at various timescales. Even if in long term it's meaningless, it may still matter when trying to make best of the finite carryable supplies while in hostile territory.
Finally not every mechanics is necessarily functional, sometimes main reason for including it is flavour (remember DX:IW and its nonsensical universal ammo system?).
If your game features different quality items possibly made of exotic materials, some of which may, for example, have excellent properties, but be relatively fragile (glass?), it makes sense to reflect this mechanically for flavour resons alone, regardless of usefulness of such mechanics, though deciding whether to pack a light, sharp, but fragile glass sword, you may need to replace at great loss (pack spares, negating weight advantage?, light disposable, but shitty chitin weapon, steel, which is durable, but heavy and cannot harm supernatural creatures, or maybe silver, which is similar to steel (the weapon is still mostly steel, actually) and harms incorporeal creatures, but dulls quickly makes for interesting gameplay.
As for ammo, with weightless ammo there is no practical reason to even track it (at least common types), because you are going to accummulate it ad infinitum.
