Charm slot rarity on belts, why?

[Madcap Symphony]

Shouldn't the number of charm slots just depend on the level of the belt, not hoping to get the right enchant on it. Takes away from other buffs you could get instead on the belt. Almost would prefer the old 5 flasks from PoE1, where they are replacing the support flasks with charms here, but making an RNG game out of getting them.