.NET runs everything from desktop apps to web infrastructure to mobile games - it's a lot more encompassing than building some websites. It also integrates into a vast ecosystem with Office, SQL Server, Active Directory and is backed up by the fast-growing Azure Cloud. Most small, medium and 100% of the Fortune 500 run on .NET code and services.
HTTP/2 is just not part of Kestrel yet, which is the default new .NET Core web server. You can always use other libraries and this doesn't affect GRPC at all (which can easily generate the server from .proto stubs).
And how are the front-end wars over? Asp.net has great integration with all these modern JS frameworks, along with MVC and WebForms which are both still viable and used often. Why does there need to be a "niche" when .NET already does far more?
It seems like you found 1 missing feature and are proclaiming it a failure when the reality is that it's one of the most common frameworks today, and now also runs great on Linux. It'll be around for decades.