You call decade a substantial longevity?
Is this some kind of a joke?
Is your ability to assess being held hostage by js ecosystem expererience?
But seriously - I expect a bit more from platform that could potentially waste my life and my venture. I am still happily supporting some Java (and JSF) code that I have written for clients 15 years ago (don't you just love that sweet support fees that you get mostly for being alive and breathing ?). Meanwhile my friend that build whole company around product written in silverlight almost went bankrupt. Now after few years working in AI (going into it a bit too soon) he is trying to create same product in ... yes you guessed it, Blazor.
Maybe some people do not learn from their mistakes :)?
Maybe some people do learn, and in this case it's Microsoft, who are not repeating the same thing with Blazor as they did with Silverlight.
Silverlight was somewhat of a unique situation, as it was a platform where it heavily relied on the platform that was phasing out. (And to clarify, that "decade" is the period that Microsoft was committed to support for latest Silverlight 5. Their first version was released in 2007, so it had about 14 years of history.)
As with Java or any other languages, you can still run it if the environment it runs can be resurrected. (I would not connect that to the internet, though) And many parts of what actually powered Silverlight still thrive in a form of .Net.
I mean where they can support, Microsoft tends to keep its compatibility fairly intact, for instance modern Windows still can run many of the 32-bit binaries from early days. (And you even could do the same for 16-bit apps on a 32-bit platform, not sure if that's still possible, though.)
Silverlight came when flash was being dismantled shortly after.
Different days back then.
10 years is pretty amazing, all told, IMO.