For this question i need a technical\engineering answer.
Why are there multiple cables carrying the same voltage? Since they are wired in parallel both in the psu and in the motherboard (i checked with a volt-meter) it should suffice one cable per voltage (+ ground).
I get that some PSU have multiple rails on 12v for protecting against failures but for example the MotherBoard 20+4 pin connector is usually wired on a single rail and yet it has many wires with the same voltage.
I'm referring to ATX PSUs https://en.wikipedia.org/wiki/Power_supply_unit_(computer).