Google appears also to be fleeing California with it's recent announcement of a new 1billion campus in New York --

Sure, Google and Apple still might retain a presence in California, as well as Amazon in Washington, but for the amount of money being spent to the tune of billions outside of Washington and California I feel that the writing is on the wall for these two extremely "unfriendly to business" socialist states.

Boeing also started it's transition to South Carolina a few years back as well ... slowly pilfering it's employees from Washington a bit at a time to South Carolina.

I don't think Google or Apple is "fleeing California." Their investments in new headquarters campuses suggest otherwise. The companies are simply planning for growth and tapping into larger talent pools.

It's also worth noting that there's a lot more to a company (even a tech company) than engineers and programmers. For some things, such as ad sales or international marketing, a city like New York is a much better base of operations than a town like Mountain View or Cupertino.

Planning for growth also includes get the heck out of Tax Dodge As Soon As Possible.

East Coast is not quite as unhinged as West Coast as far as CORPORATE TAXATION is concerned.

I think all of those are true. Like many businesses, large tech giants like Google and Apple would prefer to pay lower taxes, but would also like to recruit great talent and set up shop in affluent areas.
My reasoning for expanding into those areas would probably rest on two questions:

1. Where could I build my operation and pay fewer taxes, and receive other state/local perks?

2. Which cities currently have an affluent population, and are appealing enough to attract quality engineers, developers, operations, finance, and sales personnel?

There are several cities that answer both questions, but you always have to wonder about other contributing factors (i.e. political influence, social pressures).

... but you always have to wonder about other contributing factors

Go back over the history of how the Seattle City Council has treated Amazon over the past 7 years, and you'll come up with a few or more instances of these contributing factors --

Big Corp is always going to be about the money at the end of the day, and Seattle is going to lose 10's of thousands of jobs as a result of all of their socialist ramblings by way of tax resolutions and ordinances (some even illegal and turned over by the Washington State Supreme Court) over the years.

It's as I stated above -- The writing is on the wall for some of these western state big city socialist enclaves -- Big Corp doesn't have the time for the insidious political games of these local, regional, or state ideologically hobbled leaders, and will move to a more open money making environment as a result.