It may also be that a neutral switch already exists to lock out the starter (as opposed to only being an indicator). Adding an indicator for a sensor that’s already present is cheaper/easier/higher RoI than sensing plus indicating.

I assume it's because on motorcycles dumping the clutch while in gear could have graver consequences for the rider than a fender bender.

In my experience bikes have it because lots of them are a pain in the ass to put in neutral and is easier to see the light than to feel with the clutch.

The neutral is also in between first and second, so its a bit finicky.