With 3 miles between Google <-> Caltrain, maybe a light-rail project could also help push a project like this forward (connecting the new densely populated Google housing with the rest of the area).
This so much. Public transit doesn't stand a chance if it's not accompanied with sensible zoning that favors high density near the stations. Very often I was the only rider in my VTA lightrail on my commute to Intel, passing by block after block of office parking lots.
We'll never get significant ridership on VTA light rail unless they find a way to speed it up. It's just so slow. That would require buried or elevated tracks separated from cars and pedestrians so that it can safely run at higher speeds. But building grade separated light rail tracks would take years and cost tens of billions, so politically it's a non-starter.
I do agree with your point; but traffic must very quite a bit along the line. My VTA commutes are almost always full up, to standing room only, unless I go outside of the to/from-Caltrain schedule (and even then, it's almost never empty south of Convention Center).