I feel that it has a lot to do with Windows 8. It hasn't been accepted by the masses of yet. Since most of the new PCs come with Windows 8 installed, PC users are standing pat with their Win 7 configs.
Also, for the most part there is no compelling reason to upgrade a functional PC. There has been no major chip upgrades, no major video upgrades. Those were the reasons in the past for upgrading PCs.