What's the story on this?
The story goes that in the months leading up to WMXV, There were a number of veteran Upper Mid Carders & Main Eventers (They never came out and said who the loudest voice was, but gave enough inference clues with mentioning that they've clashed with The Rock several times before for you to pick up who it is) who didn't want him in the Main Event slot and wanted to stop that altogether. Partly because The Rock, despite his instinctive grip on the business and all the ends & angles within it, was only 2 years in and still relatively young. Another part was jealousy and spite.
Vince made it clear he wanted Rock in that spot, and The Fans made it clear THEY wanted him in that spot. But it came down to whether Austin wanted him there. I don't remember the specific wording Austin used, but he came down to The Rock's locker room after hearing the complaints and basically told him "I want YOU as my partner at WrestleMania. Let's go break records."