Because you don’t have to cram 2 new desks into the expensive 1 bedroom apartment you share with your partner.
Without the commute suburbs or smaller cities offer much bigger and better spaces for less. Why pay $4.5k for that one bedroom in SOMA when you can get a 4 bedroom home in Sacramento for the same price.
It's too early too say if the historic value of cities will be replaced by the internet, IMO. YC makes each batch move to SV for a reason.