You yourself answered your own question. In the game - easily, but then the question arises: why produce a bunch of belts and / or backpacks, if you can simply increase the capacity of one virtual inventory (displayed on the character in the form of a backpack). In reality, both options are unfeasible in terms of weight and size parameters. A game is always more or less a convention, even if it is a survival simulator. There is no point in complicating it with decisions that do not correspond to reality anyway.
PS It is worth considering a couple of points. Firstly, with an equal total number of inventory slots, one universal slot is much more profitable than several specialized ones. And secondly, the option of a single inventory with the possibility of its expansion is much easier to implement technically than several specialized inventories.