Might as well go with an F-35 then, it can carry more stuff.
But is too expensive to ever risk danger-close. Whereas A-10's have had mortars fired over them in certain circumstances...
The USAF is going to have plenty of F-35's to spare, and it it can carry standoff munitions for CAS, not unlike light attack aircraft which you aren't going to be placing into direct line also.
The A-10 was designed to take a beating, it has redundancies on top of redundancies, and armored cabin and fuel tanks, you can blow half of it's tail and it will still land (tho an F-15 has landed with 1 wing ;)).
Light attack/trainers are OK but they aren't in the same league.
The A-10 can't be replaced by effectively a trainer with a light ground attack option.
The A-10 is a flying tank, it's main gun is very useful for CAS and it can carry a lot of armaments and more importantly take a lot of punishment.
The A-10 is simply not sexy, the air force doesn't want it, it might not even want to provide CAS roles in general.
The USAF offered the US army to take the A-10 fleet in house the Army doesn't want it since logistically it can't really support fixed wing aircraft at this point, maybe the marines would take it in.
The A-10 isn't expensive, it's probably the most cost efficient aircraft the US has produced since WW2, it's simply not a sexy Gen 5 FBW doodad.