I live in the South of France in a big house that costs me $800 per month. I am about a 10 min walk from the TGV station that can take me to Paris in just over 2 hours. My kids are in French pre-k, I have top notch medical insurance that costs $139 per month to cover the whole family beyond the government insurance and I don't have to worry about my wife getting harassed by urine soaked homeless people at BART stations.
I can't speak for all engineers but given that there is an entire word outside of San Franscisco, I can see zero advantage to living there. Talent is there because they have to be. I'm sure a huge percentage would rather be working from a beach in Thailand or Tulum.
As far as investors, who cares? If you have a product people want to buy, investors will come to you. It's a myth that proximity matters. There were investors long before Silicon Valley startups were a thing. Plenty of billion dollar companies founded everywhere else. At this point, San Fran and the valley are prestige locations as opposed to offering any competitive advantages.