-- One of the reasons WWE decided to build up the John Cena vs. Undertaker match in such a non-traditional way is because they didn't want to set expectations for fans that it was going to be one of the biggest matches on the show or any sort of main event.
-- While the match itself was given the green light months ago, it became apparent soon thereafter that while Undertaker could wrestle, he wouldn't be able to work a match of any great length. So the idea was created that they wanted the audience to know that Taker would be there but downplay the expectation that it would be any sort of significant match. As it turns out, Cena lost in under 3 minutes and fans realy couldn't be upset with an unadvertised match, no matter how short.
Source: Wrestling Observer Newsletter. Subscription information & prices available at f4wonline.com