Why do our Infantry/Ground Units need aerial support against insurgents? We have since Vietnam...WHY!!!!

Tyler has an article up on the Drive that describes an A-10 sortie that rescued several ground pounders.  

Question.

Why do our infantry units, correction, why have our infantry units devolved to a point where they need fire support from aerial assets when engaging enemy ground units?  Even in ambush scenarios I would expect our infantry units to repel those attacks (up to a limit of course) without support!

Even worse?

This has been the case since Vietnam!

We have yet to sort ourselves out and to work the problem of enemy ground forces being able to successfully engage our own and not only that bring heavier weight of fire to that fight.

Whether its air or artillery we always  seem to fall back on supporting fires to solve these tactical problems.

My main issue is that this will be a problem in a peer vs peer fight.

If our infantry cannot overwhelm an attacking force organically then supporting fires MIGHT NOT be available.

The idea that we'll always have an A-10 that can make passes seems like a fleeting comfort (I won't even get into the idiocy of "shows of force" that we demand of our pilots when every pass should be placing steel on target).

What say you?

Side note.  A quick remembrance of history seems to indicate (if my memory serves correct) that this whole thing started with small unit activity in Vietnam.  You would have USMC Force Recon units operating far from supporting elements and they would sometimes engage battalion sized NVA and of course you'd have air support stacked above them providing support. The same applied to SEALs, Green Berets and Rangers.  This is how it started but also remember that these were SMALL units.  I'm talking about sometimes 3 or 6 men total.  That was the genesis of this whole thing.