I'm not going to work for any place that hires software developers based on which language they are most familiar with at this moment. As though a competent developer can't pick up a new language in a few weeks.
Well it isn't just the language that would be of interest, it's the APIs and the existing libraries that are domainspecific that takes time learning. I find it very reasonable for recruiters to look for people knowledgeable in the programming language(s) that their clients utilize in their production since those developers will most often be quicker in their job.
Sure, you can pick up C# in a few weeks, but there's no way to become a competent .Net developer in 3 weeks. It's not that it's difficult to learn, but there is so much to learn. In 3 weeks you may be able to drag and drop and autogenerate enough stuff but serious development would take much longer for someone with no experience.
The same could be said about Ruby, Python, Node, etc.