Good question. I suggest you read first Charlotte Cotton's book "The photograph as contemporary art." It's one of the best and simplest introductory book I've seen about all the post-Shore / post-Eggleston photography, i.e. color, ordinary life, intimacy, deadpan, etc. You'll find lots of people doing large format, but none of them doing contact prints on Azo, so to speak.

There are many fundamental rifts. One is of course the B&W/color divide. (I always blame it on the fact that none of these people managed to print a decent B&W print, and only produced soot and chalk crap in their art school years. But I'm casting aspersions, and I don't really believe what I'm saying anyway. ). But there is also the aesthetic/conceptual one; the objective/subjective one; the conservative/avant-garde one; sharp/fuzzy, etc.

I think that to explain the post-1970 rift, one has to look at it in terms of what happened before. Even though we all admire the great B&W photographers of the 60s, they did not have then the recognition they have now. In fact, the status of photography as a bona fide artform was still in question.

The color photographers did something interesting: they wanted access to the rarefied realms of the gallery, but chose the language that was as far as possible from it (color), instead of the one that was closer (B&W). High art always like to reinvigorate itself from a healthy dose of blue collar rightenousness. But it does so in its own terms: the photographs were not snapshots, they were using the forms of it. The vernacular was made self-aware.

The huge tension between color photography (valued as cheap, disposable, mass-produced prints) and artistic attitudes probably more contributed than countered the acceptance of color photos in the artworld. When you enter the artworld, it's always better to do it with a lot of noise than gradually.

Of course, you also have to add to this the role of Pop and conceptual art in the process of changing the attitudes towards the artefacts of artworks. Pop and conceptual art play down the value of the artwork as precious, exciting, and rare by presenting the banal or the unfazing. The status of color photograph made it a perfect candidate for appropriation by that attitude.

So why did the color photographers shook the artworld more than the B&W ones? To me, it seems that they took more risks, but at the same time played correctly the potential of changes in attitudes.

In a way, this is somewhat similar to the rift caused by the f64 people at their beginnings: they were avant-gardist, throwing sharp prints in the face of pictorialism and making all sorts of monkey noises. Our attitude towards them have changed, and they don't feel as edgy to their public now than they did before.

The same thing will happen with the colour enfants terribles. Alec Soth once had a cool post on his blog about the use of photos like his or Nan Goldin's for book cover. Of course, when you end up as a book cover, that does not mean that your art is worth squat, but it means that its shock value has been partially absorbed.

So perhaps the processes of history more than the processes of aesthetics can explain this current rift. There is nothing about it that makes it essential, it's only a produce of circumstances.