Google makes heavy use of userspace networking. I was there roughly a decade ago. At least at that time, a major factor is the choice of userspace over kernel networking was time to deployment. Services like the ones described above were built on the monorepo, and could be deployed in seconds at the touch of a button.
Meanwhile, Google had a building full of people maintaining the Google kernel (eg, maintaining rejected or unsubmitted patches that were critical for business reasons), and it took many months to do a kernel release.
Yes. I don't think anyone is disputing that Google does significant userspace networking things. But the premise of this thread is that "ordinary" (ie: non-network-infrastructure --- SDN, load balancer, routing) applications, things that would normally just get BSD sockets, are based on userspace networking. That seems not to be the case.
Meanwhile, Google had a building full of people maintaining the Google kernel (eg, maintaining rejected or unsubmitted patches that were critical for business reasons), and it took many months to do a kernel release.