I think for me it's the lack of anything that stands out that is the problem. I've looked at the other Eggleston photos on the Getty page and they are much more interesting. Like the Stephen Shore photo posted a while ago, the problem with such pictures, in my opinion, is that they function against a specific background (like ordinary words suddenly taking violent meanings in precise contexts). It was probably a bold statement to put such an "ordinary" photo in a gallery a while ago.
Come to think of it, there is one thing that attracts my attention: it's too perfectly ordinary. Most of the time family snapshots have a flaw that exudes some dynamism: overexposure, blur, expressions, bad framing, etc. Here, all these "defects" are carefully ironed out: the light is perfect, no blur, proportionate framing, etc.
It's more interesting now, in a very subtle way, though, but more than I thought at first sight...
I would consider this to be a flaw as I stated above: 3 rungs of the fence appear to "grow" out of the top and sides of the woman's head.