According to both Dave Meltzer and Bryan Alvarez of F4WOnline.com, CM Punk was reportedly not happy about the idea of facing Triple H at WrestleMania, as Punk feels Triple H is not his idea of "a big feud and a big match" for 'Mania.
Prior to his walking out on WWE Monday night at Raw, creative plans called for CM Punk to face Kane at Elimination Chamber, as the seeds for that feud have been planted for awhile now. This of course is part of a bigger story line of Punk feuding with The Authority as a whole, and would eventually lead to Punk facing Triple H at WrestleMania. It's likely Punk was turned off by the whole creative plan of him working Kane at Elimination Chamber and then Triple H at 'Mania.
As far as the backstage reaction to Punk's WWE walk out is concerned, it's being said that Vince McMahon wants Punk back, while Triple H has mixed feelings on the idea. HHH feels Punk's actions on Monday were disrespectful, however, it's being said that HHH is allowing Vince to handle the situation going forward.