Or a different “feel” when turned on vs. off (more resistance or something). They spent effort printing all that text to show where the switch was when a universal 0/1 would have made it clear.
I can’t think of any example of a button or switch that by itself can be clear if it is engaged or not. A button could be assumed to be on if in, but that isn’t always the case, like for example with emergency stops.
True of many things we take for granted now. It would be a different world entirely. Another non-computer example would be the 3-point seat belt that Volvo left as an open patent, saving countless lives over the past decades.