It's no secret that WWE makes last-minute changes to shows but during the Cruiserweight Championship match at the WrestleMania Kickoff show, the company decided that Brock Lesnar vs. Seth Rollins for the Universal Championship would open the show.
According to Dave Meltzer on Wrestling Observer Radio, the match wasn't originally going to go on first and this is why Hulk Hogan was so surprised when Paul Heyman made his way out to the ring.
The reason for the change isn't clear but speculation points to it being down to Lesnar wanting to fly home early in the day rather than having to wait around for hours during what was an extremely overlong WrestleMania. As for the rest of the card, that reportedly went ahead as planned.