We're told coming into the week Triple H wanted to go over in his bout with Brock Lesnar with help from Shawn Michaels. The thinking would be Michaels would be looking to get revenge on Lesnar. However, as of this writing, Michaels has not agreed to appear at Wrestlemania 29.
While things like this are usually sorted out far in advance, sources close to Triple H says he's simply been overworked. From securing Bruno Sammartino for the WWE Hall of Fame, worrying about whether or not they were going to be able to land Undertaker and now trying to get Arnold Schwarzenegger to induct Bruno and getting his close friend Shawn Michaels to work the show.
There are some in the company that wonder why The Rock and Brock would both go under at Wrestlemania if they're supposed to face each other at a later date.