I too am baffled by the new lack of AI expansion.
I was playing v146 and they did the typical spam settler tactic, even without accompanying units.
In 149, Rome, Arabia, Harold, Germany, Darius, and even Russia kept at 1 city until turn 80 or so.
Alexander was an exception and Iroquois started expanding around turn 30 to 3 cities each. They usually go to about 10 cities by turn 100.
What are they doing?
They weren't building wonders as I took my leisure and gave them a change to have a head start.
Scouting revealed that they had very large armies on their territories. Spearmen and archers mostly. Later, levies.
Scouts revealed a lack of barbs in middle of map locations making the accompaniment issue moot. I spend my free time running about with horsemen and scouts to kill barb camps.
When several civs declared war on me, their attack was anemic. They kept their armies on their territory.
The AI scouts were all over and their armies were quite active. They certainly knew where the barbs and best spots were.
One would guess they were preparing for an invasion with such large defensive armies?
It certainly made the game much less challenging at the end.
By turn 110 they were scattering settlers about without accompaniment. I was at war with 2 english cities. Instead of soldiers they were sending settlers at me.
Every new city I started was accompanied with denunciations of settling near their distant single city.