What else should be top? - Applications and tools use libraries or are split up into library components ... if there were many more applications than libraries there would be a lot of NIH ...
A decade ago many of us thought that open source applications like LibreOffice and Thunderbird would dominate. Instead, open source seems to be winning everywhere in infrastructure and libraries, as companies don't want to lock into proprietary middleware anymore like Weblogic or VMware. But many (most?) applications are now web-based and closed source (e.g., Google Docs, Salesforce, Gmail, etc.).
Yes, but at the same time you'd expect each library to be used by many applications. Say you have 100 libraries, you can make 10,000 applications just by picking 1 or 2 of those 100 libraries, applications should far outnumber libraries.
Maybe applications do far outnumber libraries, but it's a fact of how people use github that everyone whose application depends on a library stars the library; as every application uses many libraries, there are many library-stars. This is a total guess, but it aligns with how I think of using stars. (though stars are separate from notifications as github documentation takes care to point out)
