Much of Silicon Valley is hardware work that literally can’t be done from home.
My own company has about 15k employees in San Jose, and we’re all back to the office full time. Many of us can’t do our jobs from home, it’s hardware work.
Just by looking at buildings and job offerings, there seems to be more hardware in the South Bay, vs. the peninsula or SF. Not sure about the Oakland area.
The article defines Silicon Valley as "Santa Clara and San Mateo counties, along with the cities of Fremont and Newark." I would have split out the first two.