For many companies, cost is not as much a factor as being able to attract top talent, and not fragmenting their offices too much by spreading teams across them.

Many people in smaller metro areas that you mentioned are able to relocate to the West Coast, and many people actually do. The are no visa or immigration issues for them.

If the choice for a new location is between Vancouver and Mississippi, literally anyone in the world can work in Vancouver easily, expanding their potential hiring talent pool. Whereas a Mississippi office only attracts people that are unwilling to relocate to the bigger metro areas within the US. Any new location in the US has to deal with these new immigration issues if they don't find an exact match or if they have to hire a foreign born grad from one of the schools you mentioned. Vancouver does not have these issues.