Coastal cities have other advantages too. Better weather, favorable access to trade, better access to travel. Software could arguably be made anywhere but that severely discounts the importance of face to face communication. It's "only" a 4 hour flight from SF to Kansas City but if you're in KC and trying to work with partners in Asia that's an extra 8 hours of travel for each trip which effectively costs you a day. Make that trip several times a year and that cost becomes untenable.
