Why a Reverse Valve Body?

Those answers are good, but the main reason is to prevent disaster.

You are pumped, and your adrenalin sky high, so you go to high gear, woops, that is neutral, or worse yet, reverse.

By shifting away from disaster (neutral/reverse/park) the worst thing that can happen is to go into a higher gear and bog or slow down.

I learned this the hard way, by trying to be macho man and shift with a column shifter.
Also, one time the early Hurst Quarter Sticks had a blue cable that turned out to be defective, and my 383 went in the trees, and the monster tach memory said over 10gs.