A better question, why was Hillary campaigning in California AT ALL?
The founding fathers were indeed geniuses to create the Electoral College elsewise the person Ca.wanted as president would be president of the entire country. Given the absolutely horrible and corrupt condition of Ca. would we really want nationwide what they have?
Clinton campaigned in California, which wasn’t even in contention between her and Trump, and she achieved there an enormous victory-margin over Trump, of 4,269,978 votes; she won that state by 61.73%, compared to Trump’s 31.62%. She won that state by 4,269,977 votes more than were needed for her to win the state.
In all other states than California, Clinton lost nationwide by a total of 1,401,459 votes. However, because of her massive 4,269,978-vote win of California, she won the popular vote nationwide by 2,868,519 votes. If the election were to have been decided by popular votes instead of Electoral College votes, we’d have the President whom Californians overwhelmingly preferred, not the President whom the residents of the other 49 states strongly preferred; we’d have a President who was chosen by Californians, ruling over all of the 50 states.
These figures are taken from https://en.wikipedia.org/wiki/United_States_presidential_election,_2016 as of 3 PM 2 March 2017.
Now, just for perspective lets throw in the following: Hillary margin of the popular vote in NY, IL and MA.
The grand total of the 4 states (NY, IL, MA, and CA): 7,862,198
Do we really want the people of four of the most amoral and corrupt states in the country to elect the President?