I had a look at the list, and I can see the following advantages for my library:
* License. The libraries I saw there were either GPL, LGPL or BSD. They all require attribution which I don't like. I believe it is foolish to make users include a bunch of generic legal text in their software simply because they use a specific library internally. This is especially true if you use that library in middleware that others in turn make use of; the license text blob grows huge very quickly.
* A single file library. It can't really get much easier to integrate than that, you just add the file and it works. No build system, etc.
* ANSI C. Not everyone will care about this, but ANSI C is the most portable language I am aware of, which should mean that the code will run more or less anywhere.
Those are the advantages I can see. Of course some of these points won't be important to everyone, but they are to me personally which is why I want to publish libraries in this form.