Most are not serviceable. The were sent there by START and SALT treaties, and budget cuts. They are used for parts, occasionally.
Only the BUFFs, but some BUFFs where sent by budgets cuts as well. Also 1/3 of the Bones (B-1Bs), which I suspect are being cannibalized for parts, even the original notion was to just not operate them to save on flying hour and manpower costs, but have them otherwise in nearly flight ready status.