Add in the visa/immigration issues. A large percentage of the workforce in SV is imported from outside the country. While the business wing of the Republican Party loves cheap labor, there are other wings that oppose it. Once upon a time the labor wing of the Democratic Party would have been against importing labor but the influence of that wing has waned considerably while the business wing has established itself in both major parties. If you're not a native born US citizen, a label that describes quite a few tech workers in the Valley, the left seems more aligned with your continued existence in the United States.