A very good question, and I actually subscribe to the theory that Bret Hart proferred in his book and that I think I've seen elsewhere: there was no intention of making Warrior any kind of long-term guy. WM6 was about Vince proving to everyone that he could get Hogan to do a clean job, about getting him written off for the summer, and Warrior was simply there to keep the belt warm until it could get back to Hogan.
Remember, there was talk of doing Hogan-Warrior II at Mania 7, and Hogan is making noise as early as SummerSlam (long before it seemed there was any end in sight for Warrior's title reign) about going after the title again. Nothing was ever done or said by accident on WWF television at this time, so if Hogan said it, that was definitely a plan. And there is literally no possible result to a potential Hogan-Warrior II besides Hogan getting his win back, end of discussion.
So my own personal answer is, like, negative-90 days, or whenever the WM6 main event was decided upon. It was a fait accompli from the start, and the substandard (to an almost nonsensical and completely unseen in WW(W)F history to this point) way that Warrior is booked as champion I think bears this out. He's seemingly stuck in secondary programs because that was the intention all along.