Silverlight required add-ons for all platforms to be pre-installed. That was too similar to Flash and Silvelight became obsolete as soon as these plug-ins were not going to be supported on iPad and iPhones. There was no real point anymore.

At this stage, I see Blazor as a necessity for the .Net platform to move forward on being relevant for apps that require UI. There is no real official .Net cross-platform way of building complex user interfaces.

Blazor has the advantage of being a platform on which MS can build on to bring all types of apps together: they can be OS agnostic (.NET 5.0 already runs on Win, Mac and Linux) and target web, desktop and mobile in one swoop, although it will require a few iterations to have an ecosystem rich and stable enough to work well and consistently everywhere.