Me thinks that turn radius is the major physical reason. A secondary reason is that we often neglect to practice or refine technique regarding where to start the 'turn-in' in order to make best use of the available road surface. We get complacent sometimes and treat all turns in either direction much the same. Hence, we get into a more restrictive right turn and find we're a little cramped for space. There is one other theory that seems to be gathering a lot of support - and that is; It's all about the bass, 'bout the bass, 'bout the bass. No treble.
