Cupertino schools are a draw for young families that can afford a $2.5M+ house, which is not every family in the area. I live in the area and bike to work past Nivdia HQ every day. Santa Clara used to be "cheap" and unsurprisingly it's becoming more expensive, like the cities it borders. The details on "downtown" Santa Clara are irrelevant as everyone simply drives to San Jose, Mountain view, Sunnyvale, Cupertino, etc, etc to get dinner or go hang out anyway.

Santa Clara's house prices have been trending up for many years because it's a short commute to many companies full of highly-paid people. Nvidia's recent market cap surge has little to do with it. https://www.redfin.com/zipcode/95050/housing-market