Also, Star Citizen's most recent patch (3.0) includes volumetric fog tech developed by Amazon.

Does anyone but Star Citizen use it Amazon Lumberyard?

Unity and UE4 really are the current leaders in game engine technology, CryEngine, while great, has suffered in the last four years or so and isn't a significant competitor.

If you look in the link there are six games listed. One is Star Citizen, two are (afair) by Amazon game studios, so that would leave three other games. No idea if these are just the show cases or all of them.

So, not the greatest uptake, but Amazon was always willing to give things time to mature. We'll see if they can take market share of UE4/Unity.

It's a fairly new engine and the competition is fierce. Give it some time.