Re-read the definition of "Mr Olympia".
It's the bodybuilder who "best epitomizes"... all the good the sport has to offer... yada, yada...
The Mr O is the bodybuilding "representative" to the world. It's not the best physique onstage, it's the man who best projects a clean, consistent image and who makes the most business sense.
When you step back and see it that way, every judging decision, every 'dynasty', suddenly makes sense.