Microsoft not using Blazor, their own technology, for their own websites? interesting.
I love .NET and ASP.NET Core, but I use it purely for backend. And even there, I use 3rd party libraries like Fast Endpoints (https://fast-endpoints.com/). Microsoft keeps bringing in new technologies and effectively abandoning the ones that fall out of favour (look at the progression from MVC -> Razor Pages -> Blazor). I do not blame the Microsoft Store team for not trusting the .NET team to not simply abandon Blazor as well somewhere down the line and instead opt for other technologies for the front-end.
I really don't know how to make out of it.
It started by being .NET for WebAssembly, and then it took a life of its own, with the team pushing it everywhere there is a Webview, as if the GUI civil war going on Redmond wasn't already bad enough.
Since WebForms was a victim of the "Python 2 / Python 3" like reboot of the .NET ecosystem, at very least Blazor provides a similar development experience for those folks.
For the rest of us, used to clean MVC approaches, without allergy to JavaScript, mostly working in mixed FE/BE teams, Blazor is a solution looking for a problem, not worth the additional amount of complexity layers between browser and applications.
Web Forms and JSF have taught me not to go there again.
Unless it has changed, I think GCP uses it, as do many internal dashboards.