Why is 5 volt assigned to logic 1 state and 0 assigned to ground?

Ground is a base point in every circuit.we define it's potential to 0.so GND=0 Volts.

We know that logical circuits build up with transistors and use those in saturation mode. in saturation mode we need 5 volts voltage in input to we have this mode.5 volt voltage is IC working voltage(Vcc) too. so 3-5 volt is 1 logic