There is no reason that a particular attack even cleave, should be tied to a particular weapon. It's an unnecessary deviation from 5E that serves little purpose; there's no reason that a character shouldn't be able to make a cleave attack with any melee weapon.
Eh, at the very least cleave should be restricted to slashing weapons. You can't really cleave with a spear or a quarterstaff, given the former is stabbed into a single enemy and the latter deals damage with the force of a blow directly on an enemy. You can't realistically extend those to multiple enemies unless you take multiple swings/stabs.
And it does serve a purpose: giving weapons cool, flavorful, and importantly limited usage/small effect abilities. Of all of Larian's homebrew, this is one of the best in terms of coolness-to-OPness ratio.
