Is this because a far cheaper JDAM or SLAM can do the same job?
Probably because those weapons are cheaper & more versatile with launch from multiple platforms.
No, this is because of bilateral agreements with the Russians.
No. Sorry to burst this bubble. But it is precisely what it purports to be. Unilateral disarmament. Unilateral because there are absolutely no enforcements to assure that the Russians are complying with their end of the deal. And in fact, W has bragged about doing these unilateral cuts irrespective of what Russia does...as a sign of our greater moral superiority or something.
He apparently always believed in the Leftist drivel that somehow we had too many weapons...and the Russians would follow our "gestures".
How many times have we seen the liberals issue gesture-after-gesture which were correctly interpreted as weakness by the Communists?