I think I have additional insights as to why Isaac doesn't compete. For one thing, when you look at his pictures it's quite obvious that he is actually a rather shy, humble person. He seems to be reluctant to even pose at all, and tends to keep himself pretty well covered up. He seems to be almost hiding in all those dark photos.
As further testament to his humility, Isaac has not even discussed his educational accomplishments at all, and has only briefly mentioned his significant accomplishments in the business world.
It doesn't take an Einstein to deduce that this man is very well educated; after all he is called "Dr. Size". As we all know, to be called "Dr.", one must have completed several years of advanced education beyond the undergraduate college level; this could be in the form of a PhD, MD, DC, JD, or any combination thereof.
But Isaac - being an unpretentious, practical, humble man - remains true to his roots. Rather than get wrapped up in all the red tape and baggage that the bureaucratic, highly political worlds of academia, medicine, and law offer, he chose to become a true entrepreneur in control of his own destiny.
Rather than engage himself in futile attempts to cure cancer, file class action lawsuits against big corporations, realign spinal cords, or attempt to educate snot nosed, unappreciative students, Isaac chose to make a real difference in the world around him. He has dedicated his life to providing stylish, reasonably priced clothing to the tall and fat people of this world.
Seeing that Isaac is such a practical, humble humanitarian of infinite wisdom, we can clearly see why he has chosen not to compete. His gorilla-like genes would not make competition fair at all. And if he ever decided to step over to the darkside and realize the 5-10% advantage, we'd be seeing a raw bench press of as much as 907.5 pounds, arms as large as 31.9", and a muscular bodyweight as heavy as 401.5 pounds - almost as big as the late Trevor Smith!...