Stick with program managing, Justin. Actually, given you were responsible for Silverlight, find some other career entirely.
If you check Perl, Java, PHP or C++ on Indeed.com, you will see exactly the same trends.
If you perform his same terrible analysis of the TIOBE index, PHP, C++, VB.NET, Objective-C are all going to collapse. Apparently Java has been "heading for collapse" since 2004.
People who can't do statistics shouldn't report on them.
The problem does not appear to be that C# is becoming less popular (than other languages), it's appears that custom application development as a whole is becoming less popular than it was a few years ago.
This may be due to the economy, outsourcing, mobile platforms or whatever. You can't suddenly pull reasons out of your ass like this being due to "Microsoft’s ever revolving door of new technologies", despite how pissed off you are at them for shit-canning your pet project.
When doing stats on whether something is less popular, it's helpful to ask "less popular than what". Sure, it may be less popular than it used to be, but so are the competing languages. This does not indicate that the C# ecosystem is going to collapse.