I wrote it for the classic reason: I needed that functionality, and no existing YouTube plugin would provide it. While there were a bunch of YouTube plugins, they weren’t for the sidebar, required some framework or other plugin that I couldn’t get working on my version of WordPress, or just plain wouldn’t load the videos properly.
So, my plugin. Simple and effective. Learned quite a bit about the WordPress API, too, which like most APIs at first seems bizarre and inscrutable, then feels surprisingly elegant after some use.