Silverlight was essentially a polyfill for back when browsers weren't very capable. I did a ton of work with Silverlight - streaming video, vector graphics, cross-platform front-end apps with back-end integration... all stuff that was pretty hard to do back then, but is now widely available in all modern browsers.

Also, both the JavaScript language and runtime were pretty hard to build reliable, performant apps in back when Silverlight was introduced. The JavaScript language and runtimes have matured considerably since then.

If it had been my say, I'd have kept it for a little longer than they did, but by now I'd say it's no longer necessary.

There were always two camps in the Silverlight world, both inside and outside of Microsoft: those that saw it as a way to make browser-based applications more awesome, and those that saw Silverlight as a way to get away from that yucky HTML/CSS/JS dev. I was always firmly in the first camp, and from that side of things I wouldn't take back a minute I spent on Silverlight dev - I got a jump on video, vector graphics, browser-based apps, etc., long before it was practical to do that in the browser. When those technologies hit mainstream browsers, great!

Note: Microsoft employee but definitely only speaking for myself here.

Silverlight was competition to Flash. Once the standards were far enough along that it was clear plugins weren't going to be necessary, there was no reason to keep it alive. Honestly, you should be happy that Microsoft killed off theirs and decided to use open standards instead.