Close Air Support and Power Projection, or even simple conventional carpet-bombing are entirely different things.
Obviously, dropping 16 nukes or carpet-bombing an entire city isn't something you would want to do close to your troops. And, while conventional bombs dropped from a B52 can be incredibly precise if needed, it's still not generally considered CAS simply because they're not very reactive. They have a mission that's been planned for weeks, and they take off and set up their flight plan literally the day before. CAS is reactionary and constantly evolving; an aircraft is assinged more to a particular group of soldiers to use as needed rather than having a directed mission to destroy X and Y and Z and then leave.
That's not making a claim that one is better than the other. They're just different roles with unique aircraft (and services) that can acheive them best.
