#2. He's waiting for Finn Balor to return

There was some suggestion that Finn Balor was going to take time away from WWE are requesting a small break, with that rumored to take place after SummerSlam. This led to the belief that Balor would lose against Wyatt at SummerSlam (especially after choosing not to be 'The Demon')
However whilst Balor did indeed lose to The Fiend at SummerSlam, and quite emphatically may I add, he was able to walk out of the ring via his own volition so isn't necessarily so 'injured' that he needs to take time off.
If the plan is still for Wyatt to completely write Balor off of television whilst he's away it would make sense to keep Wyatt off of a Monday Night RAW that doesn't feature Finn Balor and wait for his next appearance.
You could then cement The Fiend as a heartless and dangerous monster by having him do something legitimately terrible to Balor to write him off of WWE television for however long his break is.