Because it's simply silly to say a team should be sufficiently pumped up to be playing in a championship game. If anything, playing big games can bring out the nerves (ask your QB). A team that feeds on a crowd can have those nerves calmed and go from jacked up to playing beyond belief and that can be the difference in the game.
And when I've used it, I did so the same way you did...against a team that I really didn't want to lose to with a loud crowd that DOES make a difference in games. When you have nothing else to use, you pull out the "well, if they need to be motivated by xyz, they aren't ready to be winners...blah blah blah." It's ok man. Like I said, it's a standard, but silly retort.
Nice add there, too. IF the Eagles come out and play well, you think they will win. We happen to think they won't come out and play well, and part of the reason will be because of the crowd noise and the defense flying around enticing us to yell even louder to blow the roof off of Jiffy Pop.