It's case of https://en.wikipedia.org/wiki/Metonymy. Silicon Valley is no longer just a physical place, but also represents the tech industry itself in popular imagination. Also, while the article is centered on Microsoft, I think the title is meant to be general, as shown by this passage:

> The project represents a much wider effort to build a new breed of computing system that is truly conversational. At companies like Facebook, Amazon, and Salesforce as well as Microsoft...