I’ve hiked all over the Four Corners area and you are quite correct about the amazing number of remains in the area. They are literally everywhere, including some areas where it is hard to see how anybody ever made a living there, especially over in the Canyonlands area.
They estimate the area was a good deal more heavily populated then than now. Though, to be fair, that isn’t saying a great deal.
The spectacular cliff dwellings were a late development and weren’t inhabited all that long. They developed, IMO, because of the ongoing disintegration of Anasazi society, with resultant warfare, cannibalism, possible human sacrifice, etc.
About 20 years ago I took the official Mesa Verde NP tour and was highly amused by the official line about why they moved into the cliff dwellings after living for many centuries in far more conveniently accessed mesa-top pueblos. The line was that this had nothing whatsoever to do with their need for a defensible position, as the Anasazi were totally peaceful. Anybody but an idiot that looks at these ruins can see they were chosen for their defensive value.
This compulsion to view past societies as peaceful, when they clearly were not, tells us a great deal more about those who make such statement than it does about the past societies. They used to say about the same things about the Maya, until someone unfortunately translated their writings, which showed they glorified violence, torture, etc. Much like the Assyrians, in fact.
Your comment about the local tribes always avoiding the ruins has not been my experience. The Ute Mountain Ute tribe has the non-Park part of Mesa Verde on its reservation. They run a profitable tour business to many of the ruins on their land. The Navajos run some similar tours.
You are correct and I should have been more clear. The "traditional" Navajo will not go into what they call ghost places. I had a long discussion with a Christian Navajo who had always wanted to go into the canyons, but her husband was traditional and would not go. The Navajo do run the tours in Canyon de Chelly and I think Chaco Canyon, too. We took the Jeep tour into de Chelly. There are Navajo living inside the canyon, but we were told they do not go inside the dwellings. I don't know if that is for superstitious reasons, out of respect for the dead, or for preservation reasons - as I said, some of them get real evasive when you ask certain questions. But the Christian Navajo told me that a visit to a ghost place for a traditional Navajo would require a 5-day cleansing ritual afterwards that would cost 10 sheep! (She could have been pulling my leg, too... there's always that!)