Went to Mesa Verde last year but thankfully was not bombarded by too much eco-babble.
The cliffside structures would have been inconvenient for day to day living so there being located as a defensive decision makes sense.
As a WAT-—wild ass theory—— I wondered that since this forting-up in the Southwest occurred congruent with the Mongol era if maybe some North Asians had crossed over and ended up attacking our earlier residents.