It’s pro wrestling. Egos dictate everything. Vince McMahon won the Royal Rumble. He also became WWE champion. Vince Russo booked himself to win the WCW championship, to go over Ric Flair and never actually lost a match in that promotion! Verne Gagne once booked himself to win the AWA championship and then retired while still being the champion!
Greg Gagne had a main event feud against AWA champion Curt Hennig. In the dying days of the promotion, he was about the only one Verne could count on to not leave the sinking ship for the WWF or the NWA. But Verne Gagne still never made him his son the champ.
A testament of how serious Verne was about his business and the sanctity (!) of pro wrestling in general, even as everything was crumbling around him?
Look, the problem is that it would have made TOO MUCH money. Verne was flying under the radar as a small business, and Greg Gagne drawing 20,000 people every night would have put him into a tax bracket that he wasn't prepared to deal with. Plus then he would have had to buy out Vince and there would have been way too much paperwork to deal with.
Now, some people would tell you that in fact he tried to put the title on him several times and the local promoters refused to work with him if he went ahead with it, but they're LIARS. We know the real truth, which is that Greg was too beautiful for this business.