To those wondering about why California... I understand your sentiments, as I'm Californian myself.
But it just makes sense logistically and financially:
-California is home to Silicon Valley and Hollywood. Regarding tech and entertainment, there is no better place to go within the US. This will also let them hire from among the best of the best (staff), as Hololive is technically both an entertainment company and a tech company.
-California is home to the biggest shipping port in the US, LA. Logistically speaking, if they want to curtail shipping costs, it would make sense to set up shop in LA (presumably where they're establishing a base).
-Distance-wise, California is the closest state to Japan other than Alaska or Hawaii
-California is home to some of the largest metro areas/cities in the US (LA, San Diego, San Jose, San Francisco, Oakland, Fresno, etc.)
-California probably has the largest concentration of weebs/vtubers in the US
-It's not too far from British Colombia, which is where are lot of Canadian vtubers are located
-Most populous US state
-Close to Mexico if they ever attempt a Spanish branch (and California has plenty of Spanish speakers)
We can only hope they vet their staff properly, but I have faith in Hololive (due to its track record).