Greater supply of employees, and potentially greater attraction TO employees.

Sure, they have to "import" employees, but importing 10% of the workforce in the Bay Area at X cost is apparently more appealing than importing 98% of employees to Tulsa at Y cost.

(Relatedly; Tulsa's not exactly a small place, but if you think the influence of "big tech" is bad in a larger metro like the Bay Area, I'd HATE to see what it would look like to bring a deluge of 'outsiders' into a much less populous region)