Originally Posted by kickstart

You don't seem to understand.

One typically signals with their left hand, which naturally leaves the right for braking.

The rear brake is more forgiving of over braking, as such it gives one a greater margin of error when braking under challenging conditions.

It has nothing to do with what one is used to or what side the lever is on, it's just the natural dynamics of a bicycles brakes.

Therefore it makes sense to have the rear brake on the side one is likely to be using when braking with only one hand on the bars.