What happened with Silicon Valley is that the ease of working remotely increased, but the pace at which new innovations are discovered and commercialized increased more, which means that the returns to moving really fast (which usually means a colocated team, to cut out travel/timezone delays) went way up. It doesn't matter if you can save 30% on labor costs if it means that you miss out on a $100B market that just opened up.
If you read Carlota Perez, this trend usually reverses itself in the "deployment" phase of a new technology, where market structure has stabilized, best practices become widely known, and the expertise surrounding the technology becomes distributed geographically. For example, the deployment phase for mass production (initially a Massachusetts monopoly in the U.S. in the 1830s and 1840s) came as the great Midwest steel mills and factories were built in the 1890s, the deployment phase for railroads (initially a Midwest & Northeast thing in the 1850s & 1860s) came in the 1910s as railroads were completed linking the South & California into the nationwide network, the deployment phase for automobiles (a Detroit thing in 1900) came in the 1950s and 1960s as suburbs spread throughout the U.S.
The catch is that usually the transition from "frenzy" phase to "deployment" phase is marked by a financial crisis, depression, and war. If the new geographic region was on the same side of the war as the new means of production (as with the U.S. after WW2), then the mechanism of diffusion is usually that lots of people are trained in the new technologies as part of the war effort, and when they go home, they bring these technologies with them and start up new businesses that become part of the fabric of the local economy. If the tech monopoly is on the opposite side of the war as the new geographic regions (as with the U.S Civil War, or Asia post-WW2), it's usually because the side with better technology won the war, conquered everyone who resisted, and a bunch of carpet-baggers move into the occupied territories, bring their technology with them, and then integrate with the economies they left behind.
I assumed its really due to a lack of well paying jobs, combined with an increased debt burden from college.
I guess one could argue technology has lead to increased automation and reduction of jobs typically found outside of cities.
Close. It's because there's been a massive reduction in low-skill jobs that can still pay the bills outside of cities (whose size sustains their service sector, so you can keep the people who can't cut it at university employed).
Robotics did this somewhat; Chinese slave labor doesn't help.