Everyone is using Kubernetes, yes. Few are using Kubernetes for high scale production workloads. This will change within the next 2-3 years, of course, but there is a massive amounts of inertia at many of the companies that you've mentioned from moving away from traditional server based workloads.
Scroll down to Case studies; https://kubernetes.io/case-studies/ - there are far more large corps using it that aren't listed on this of course. I'll let them toot their horns if they'd like. :)
Also, as I work with k8s I like to watch the trend of HNs "Who's hiring?" threads out of curiosity and I ctrl-f for kubernetes/k8s. Last few times I've looked 20-25+ have had kubernetes in their postings. It's been a pretty fair chunk / near-majority over the last 6 months or so.
It's a marked difference from when I got on the kubernetes train around 2015, that's for sure!
They all do. Major tech companies have money to burn. Name a trendy tech that BusinessWeek or WallStreetJournal says will "transform the industry" and some schmuck exec will decree they need to be using it.
