You may want to handle more data because the input device(s) can produce it and you need it. A mouse wouldn’t but a VR controller in 3d might. Or a keyboard + mouse could produce a 3d vector for a flight system. All in one neat node.
It also meshes with swizzling - remapping XYZ to YZX, for example - right inside the input itself. So you can use the resulting value as is, without lots of wires snaking around and confusing things. Can be done with 2d vector, too.