I guess they're not that shy, because they are filming themselves singing songs and then uploading the clips to YouTube.
There's an entire subgenre of young females strumming their guitars, usually in their bedrooms, and singing about the nerdiest things imaginable, from StarCraft to physics. Many of them do a wonderful job, too.
Kotaku's posted these types of tunes before, such as Allie Goertz's little ditty about Dungeons & Dragons, which is so sentimental that I've posted it here again. Consider it an encore.