I have an idea as to why BG3 might be restricted to one melee and one ranged weapon, though it's just a theory.
BG3 doesn't have equipment loadouts as such - the game doesn't recognise what you hold in your hands or what is equipped but shiefed. So for example if you equip shield you will get bonus from it, even if you switch to ranged.
Think of how hotbar work - you can directly access both ranged and melee skills and there is no way to specify what weapon you would want to use them for.
Imagine you have a worrier with multiple melee weapon equipped - how would you specify which weapon you want to use for manecing strike? The game doesn't support something like that. That's why every skill using both melee and ranged weapons has both ranged and melee versions.
Not an implementation of which I am fan of, as generally characters will specialize and stick to one, and having same category of weapons with different damage types would be more beneficial.
