My theory is simple. He never had to learn the fundamentals because he bullied all the other kids at youth level due to his size and pace.
He could just kick and rush, or bundle / bulldoze his way through smaller players.
This worked and still worked as he grew older but there are glaring, fundamental deficiencies in his ability, it's frankly startling someone can get so rich, being this abjectly bad.
Before anyone harps on about his record, I'd say that is more a reflection on the players he played with, a massive compliment to them indeed!