Because there is value in having people in personal contact, especially if they are expected to work in a team. I don't know what I'd do if I didn't have the option of dropping by a coworkers office for a 5 min quick chat or a 3 hour informal meeting on a whim, where we might pull out our notebooks and pull up relevant files and email threads. Deep thinking can't happen on a slack channel, it happens during the skull session.

California is also a powerhouse of a state. It has the 5th largest economy in the world, and the most productive state government in the U.S. Ambitious projects actually get attempted and built in California unlike so many of the stagnant states in the U.S. Another reason of why SV and not Idaho is the academic research environment of the bay area and the ease of recruiting the excellent talent that comes out of California's universities every spring.