From Wikipedia:
In 2013, Microsoft announced that they had ceased development of Silverlight except for patches and bugfixes. Microsoft announced the end of life of Silverlight 5 in 2012. Silverlight is no longer supported in Chrome on OS X, while support for Silverlight in Chrome on all other operating systems will be disabled by default in April 2015 and removed completely in September 2015. Microsoft has set the support end date for Silverlight 5 to be October 2021.
Since it is not Open Source it will not appear in the Pi (and Moonlight is a sad joke).
This is standard Microsoft MO. Produce a competing version of something that is popular and use it to fragment the market. Once it has done its job, kill it.
We can see examples of that even today.