Horizon Zero Dawn limits you to four weapons on your character at a time – but you can swap them out for extra weapons in your inventory at any time. Eh?
Horizon Zero Dawn lets you carry multiple weapons in your inventory. I think it’s six or eight.
However during gameplay, you can only carry four of those weapons. This isn’t a true limitation though, because at any point you can pause the game, go into your inventory and swap them.
Thus, in practical terms you have access to any of your weapons at any time, but only if you go through the rigmarole of inventory management.
Why have the inventory stage at all? By letting me swap quickly between any weapon as you’re fighting, you’d encourage people to experiment in gameplay.