There are plenty of reasons trees might fail to thrive here: long dry season, masses of clay, thick limestone/caliche (we dug through two solid feet of it then couldn't get any deeper with our tools), unfriendly pH, etc.
Many of the trees I've dug up are root bound - their roots are growing in tight circles rather than out. Usually this happens when a tree is in a container too long, and its roots are bound by it. But it also happens when a tree is planted with a parcel of soil into an unfriendly location, and the roots just grow around and around within that bit of soil that it came with.
We'll be watching this dozen-ish trees (along with the rest on the land) and some may need to move again, or at least move into larger holes that have a larger amended environment. I've added aged cow manure, but haven't done anything to change pH, e.g.
What a natural response, to keep growing and growing in ways and places that are comfortable.