IIS dying and Nginx replacing it might be due to Microsoft encouraging the use of Nginx with .NET (the artist formerly known as .NET core) ASP servers.

.NET already has a server embedded in it (Kestrel) but Microsoft documentation points to Nginx as the solution once you've moved out of development and into the wild, when deploying on linux.

https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy...

I'd also assume the heavy use of CloudFlare makes gathering statistics extremely difficult.