In additon, some level of regional redundancy is critical to prepare for black swan events (eg. a regional power outage like in the NE in 1996, flooding in Sacramento or East Bay suburbs leading to Product Owners or feature owners dealing with evacuations - this happened to us with the current flooding).
And finally, 24 hour operations allows you to expand to markets outside the US. While engineers in San Jose are sleeping, it's the middle of the workday for customers in London, Paris, Istanbul for example and they will inevitabely have bugs and issues arise.
Also, like I mentioned in the comment below:
2. Training and mentoring is a reflection of your company's Engineering Management. My employer has had an easy time offshoring development to Slovakia and Bangalore because we had Tech Leads and Engineering Management make the initiative to mentor, train, and onboard offshore team employees as we would domestic employees. I've seen similar examples occur across the industry (eg. Google Pay's dev team in Hyderabad, DE Shaw's dev team in Gurgaon, Motive/KeepTruckin dev teams in Lahore & Islamabad). If Management views Engineering as a cost center (which, it pains for me to say as an ex-cybersecurity engineer, at times it can be), that's where you tend to see the relationship between offshore and onshore teams collapse, because the relationship is based on the implicit arbitrage of labor.