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Among a certain class of antitrust commentator, there is a link between firm concentration and the decline of regional hubs. They always cite one Washington Monthly story. Could be true! But I'm skeptical and this story gets at why https://www.wsj.com/articles/low-taxes-and-high-temperatures-lure-finance-firms-to-miami-11609851600
Big firms (here Goldman Sachs and Blackstone) frequently decentralize. Amazon and Google spread across the country. In contrast, small firms and start ups often need deep labor markets in their area, spillovers, etc.
As @Richard_Florida regularly points out, VC and start up funding is still very concentrated, more than tech employment https://www.theguardian.com/technology/2020/dec/20/texas-silicon-valley-austin-tech-workers
The other side of the market is important too (and more important for land use questions). In bigger cities, firms have much less monopsony power over labor. Here is @mioana @joseazar @Econ_Marshall https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3088767
