Since Thiel doesn't have the celebrity status of the aforementioned two hopefully he won't stand a chance. On the other hand, since Bush Jr and Trump got elected it's obvious that anyone can.
But not everyone buys this. Another explanation is just that California is 38% non-hispanic white and falling. [2][3]
[1] http://www.latinodecisions.com/blog/2013/10/17/prop187effect...
[2] http://www.motherjones.com/kevin-drum/2016/06/california-and...
[3] https://en.wikipedia.org/wiki/Demographics_of_California
Looking backwards, there was little difference between Davis and Schwarzenegger.
This is also true for Massachusetts. The people are smart enough to know party doesn't matter, but the person's ideals and what they have to offer. Also not all the people who vote for President will vote in local elections.
Bear in mind that a conservative running for President has to turn out conservatives in Ohio and conservatives in Florida.
There are issues on which California voters are conservative (or at least, favor positions usually held by Republicans - not quite the same thing but I won't quibble). We just voted again in favor of the death penalty, for instance.
Conservatives running in only California get to tailor their message to those issues, while on other issues being willing to compromise or even genuinely differing with other Republicans (see Schwarzenegger on climate, for instance).
Because the state's demographics and industry changed...? California was hardly a liberal bastion before it became solidly blue on the national level in 1992.
Even then Schwarzenegger was hardly a conservative compared to national Republicans even in 2003. And he pivoted even further left before his 2006 re-election bid.
Where you could see the difference would be in the California assembly and senate and at the federal level in the House of Representatives since that depends on how districts are defined.
I.e. Where the people actually live. The only real big metropolitan area that isn't coastal is Sacramento.