Well yeah. That’s just the natural math of a growing city. Out of town becomes the ex-urbs, ex-urbs become suburbs, and suburbs become urbs. Not really a mystery. At the end of the 19th century the part of Tucson I live in was a different township entirely with a bunch of nothing between it and Tucson. By the time I got here it was all Tucson.
Lots of things didn’t exist yet in the late 1800s