Put another way, restricting housing supply in Mountain View likely impacts rents its socioeconomically similar neighbor, Sunnyvale.
Among likely differentiators: 1.) Traffic. If you're traveling to Google or Facebook Sunnyvale adds an extra 15-20 minutes to your commute. 2.) Schools. They're better in Mountain View, at least for now, though both regions are rapidly gentrifying. 3.) Cachet. Mountain View has the name because of Google. Sunnyvale doesn't really, and also feels like more of a sterile suburb than a lively community. 4.) Shuttle stops. I don't know exactly where they are now, but that'd explain why the downtown areas go for relatively equal expensive rents, while my neighborhood (which AFAICT has no tech shuttle stops anywhere near it) rents for a lot less than other neighborhoods in the area.
I definitely don't have a nuanced enough understanding of the difference in civic liveliness of the two cities - and resulting desirability - they both always felt pretty suburban to me. But I've never lived in either one.