A lot of developers don't want to write the core (and sometimes complex) business logic in Javascript, and thus this allows writing client applications that take advantage of all the .net framework with strict compile time checking that is better than Typescript.

On the other hand of the coin a lot of developers in the frontend and design related space are experienced with HTML, CSS, and some javascript and therefore it gives the same advantage that Blend gave for WPF, it makes it easy for frontend folks make the application look good while the C# folks can make an application function well.