F-16s almost got the job once, but the USA(rmy) played a major role in keeping them in service. Actually, for a time the Army was going to GET them and fly them themselves, but it never happened (JMHO but that was probably the best idea yet).
Hang.. they weren't mothballed. Hoever Desert Storm stalled that from happening for... oh about 11 years so far. The F-16 was all set up to take over CAS. The Army screamed to high heaven about it and won.
Remember, the USAF is run by a bunch of Generals, most of which don't know all that much about CAS or care too. And pretty much none of them have one singular iota of a clue what ground combat is. They got this goofy idea that CAS can be coordinated with F-16's from 20k feet... ahhh, no. Likely they'll think the same thing when the JSF hits the air, ... ahhh, maybe. Trust me on this, F-16's have a hard enough time hitting stationary targets that they have coordinates for, I'd hate to be in a ground unit about to get over-run knowing all I had for support was a couple F-16's... egad.