There is a C-130 variant for ground attack, as well as kits the marines use to turn a C-130J into a ground attack craft. But the C-130 is very big and very slow, so you need absolute dominance of the skies and you need to make sure you've cleared out all the ground based AA.

85 ton B1 vs. 35 ton C130.

It doesn't matter that much if you are going 720 knots or 320 knots if you get shot by BUK missile traveling 2000 knots. Both C-130 and B1 can fly above small caliber Anti-air artillery range and above MANPAD range with ease. Nothing can fly above BUK, you would need stealth to operate at those environments.

The only threat where B1 is clearly better is if you get shot by Flack 88. But that's not going to happen. So B1 gets phased out as too expensive platform.