#3 Predictable outcome
There was no way that Braun Strowman was going to beat Brock Lesnar at the Royal Rumble. Having protected Brock Lesnar for as long as they have, it wouldn't have made sense for WWE to book a title change at the Royal Rumble.
And therefore, we all knew the outcome for the Lesnar vs. Strowman match going into the said match. How many of us were genuinely excited at the prospect of such an encounter?
If you consider the fact that Seth Rollins vs. Lesnar has been rumoured to be the Universal Championship match at WrestleMania, which seems like a match with actual heat, Strowman vs. Lesnar does not seem like an exciting match at all. It would have been a very predictable affair.
Is it any wonder then that WWE didn't think twice about cancelling the title match?