The USA as a whole is center right, which inhibits unionization, especially for privileged white collar groups, so you only see unionization for lower paid blue collar jobs in SV. It has very little to do with the local degree of leftism.
This might give a better indication of the way things are in SV:
http://www.mercurynews.com/2017/07/24/hundreds-of-facebook-c...
http://blog.sfgate.com/techchron/2015/02/23/facebook-bus-dri...
The USA as a whole is center right, which inhibits unionization, especially for privileged white collar groups, so you only see unionization for lower paid blue collar jobs in SV. It has very little to do with the local degree of leftism.
This might give a better indication of the way things are in SV:
http://money.cnn.com/2016/06/06/technology/crowdpac-donation...