#4 Last-minute change of plans
People need to realize that WrestleMania 35 was essentially written and planned with the full expectations that Roman Reigns would not be a part of the event. It probably wouldn't be surprising if WWE wrote stories for the entire year without expecting Reigns to return.
After all, when he announced that he was diagnosed with leukaemia again, many people estimated that he would be out up until early 2020 at the very least. However, no one expected that he would be back in time for WrestleMania 35.
This was probably why there was quite a bit of shuffling going on with the plans. WWE probably listed out a few opponents for him, and perhaps even locked in a match or two. However, in the last minute, the build was changed and Reigns will now be taking on Drew McIntyre in a battle of two hosses of WWE.