In Boston's case specifically, the Big Dig did improve the living experience--after a fairly long period of time. (And there were some incremental public transit improvements.) But many US cities also had reduced crime rates and other quality of living improvements, the exact reasons for which are still debated and which led to many employment opportunities returning to cities.

My former company opened a relatively large near-downtown office and, while they're keeping a suburban office, it will be much reduced from its earlier main location.

I think partially it was because it was so cheap. In the late 90s I had an apartment a block from the lake in the Lakeview neighborhood in the Chicago north side and it cost $400 a month. Before that I lived out in the Chicago suburbs and my apartment was $800 a month.

That was a steal. I lived in Lakeview from 1995 to 2000 (with a brief detour in San Francisco) and every place we rented was north of $1500, nowhere near the lake.