#1 There's no better match on RAW for Roman Reigns
This is the most likely reason why Roman Reigns vs Drew McIntyre is happening. After Reigns returned, WWE looked at the list of opponents, that likely included names such as Kurt Angle, Braun Strowman, Baron Corbin, Drew McIntyre, etc. and felt that there was a story to be told with McIntyre.
After all, Strowman vs Reigns has been done to death, Corbin vs Reigns is underwhelming, while WWE probably felt that Angle vs Reigns wouldn't be a good fit. While we disagree, this is certainly an interesting spot, and one that fans won't really complain about. In fact, it's the first singles match that Reigns has ever had at WrestleMania that isn't against a part-timer.
A top AEW star just called one of his colleagues 'spoiled' and 'narcissistic' HERE.
His previous opponents were Brock Lesnar (twice), Triple H and The Undertaker. He's 2-2 and will most likely end up going 3-2. It's a good match between two great full-time superstars.