I'm pretty sure the accumulation of capital that draws people to SV and New York. There were numerous studies, e.g.
https://www.researchgate.net/publication/228200217_The_Geogr... . That's why it is really hard to set foot 50 miles further than the centre of VCs, not because it is harder to attract talent.)
“In Connecticut and Massachusetts the proportion of investments located within 50 miles of the investor’s home or office is 37% (Freear et al, 1992). In New England the equivalent proportion is 58% (Wetzel, 1981) while in Ottawa the proportion is 85% (this high proportion reflecting its proximity to different cultural and political milieus to the north and south and distance from other major urban areas in English-speaking Canada). In the UK, Mason and Harrison (1994) found that two-thirds of investments by UK business angels were made within 100 miles of home.” http://strathprints.strath.ac.uk/15803/
This slowly changes, but still, matters.