The problem is not that they couldn't, but they wouldn't. Most of the large bay area companies believe that there is more value in the chit-chat and overheard conversations at the micro kitchen, than in solving the remote work problems.
Working remotely requires a lot of attention to relationships in ways and over channels that most people aren't accustomed to. It can be difficult even for people who are very good at it. I enjoy working remotely but I value the personal face-to-face time I get with co-workers very highly.