Although Microsoft would never admit as much, the classic .NET framework is already a legacy product.
All their investments into .NET over the last couple of years have been for .NET Core - this goes for all of the internal performance improvements (that allow e.g. Bing to use .NET Core), new foundational paradigms (such as pipelines and span/memory) that enable entirely new classes of programs to be written in C# (and still be performant), and complete reimplementations of some of the most popular frameworks (MVC, SignalR, EF).
The fact that very few of these investments are backported to classic .NET should tell you a lot about which framework is a dead-end and which one is not.