The real reason why bb'ing is full of short guys would be because if they were taller, and still had some size, then they'd be capable of doing other sports at a pro level...if they had the talent.
Pro bodybuilding is never a first choice for the top pros...well, perhaps Arnold but let's be honest, that was another time.
Of course, the 'perfect' sized bodybuilder is around 5'9. Most density on that frame, unless the tall guy has the right genetics. Which is why the taller guy almost (and I really mean 'always') beats the shorter guy on stage.
Now on with the boobies.