It is all because the Eagles' management has done a piss poor job over the last 5 years.
Take a look at the Birds' WRs. Come on, Avant, Lewis, Brown? All those guys would have even been cut from the Cincinnati Bungles and the St. Louis Lambs. Philly fans are being totally unreasonable asking McNabb to carry the Eagles to the Superbowl with a WR unit like that. McNabb is a QB in the NFL, he isn't a miracle worker that can squeeze blood from a stone.
Philly desperately needs a probowl caliber WR and a good TE. A good WR will open up the field for Kevin Curtis and will spread the defense out. This would give much more room for Westbrook to run. But alas, the Eagles' management has refused to spend money on a WR, and they are now paying the price.
Look at what happened when we actually spent some money on a good WR. McNabb had the best year of his career by far, put up insane stats, and finished with a 104.7 QB rating which is absolutely filthy.