It actually looks more like people don't use Facebook nearly as much in general? I don't think this data supports the suggestion that people in Silicon Valley don't click on ads, they also have very low comment, like, and share frequency as well. I think active time on site per user in Silicon Valley is just lower than the national medians.

Also note that this seems to be rounded up to the nearest whole number, so we can't figure out like:ad click ratio or something like that from the data.