My husband is a UC Berkeley grad who works in technology and he says that Silicon Valley wouldn’t have seemed like a natural fit for start-ups in the early days either. Apparently, what it had going for it was being close enough to SF to attract a lot of Stanford and Berkeley graduates and inexpensive land for building fabrication plants. The Philly metro area has some great schools that churn out a lot of graduates, is conveniently located on the I95 corridor, has an airport with direct routes to major international hubs, and each funding round can probably last longer due to the lower rents and cost of living compared to other major cities.