Why kicad schematics pin electrical type is always power input?
VCC and GND are meant to be power inputs. ERC on the schematic will check that all power inputs are driven i.e. have a power output somewhere on the net. It'll also make sure you don't connect two power outputs together. An example of a power output would be the output terminal of a regulator.

The idea starts to break down if you put passives (inductors, chokes, resistors) that break up the net, but it can be helpful when used properly.