Agreed, California is an odd place to choose as a launch site. The only benefit to it might be ease of transferring materials.
Arguably one reason the Maldives in the Indian Ocean nor the Line Islands in the Pacific Ocean have not been developed as a possible launch site. Even with the use of the oceans, the logistics of distance and time is a powerful foe.
The other, regardless of downrange issues, everyone wants it in the back yard. There the government can keep all the secrets safe and well protected, and once the fireworks of launch is over everyone else can go home eat Bar-b-Que and sip cold beer.