I know benefits of using cdn for ones website and I have been using cdn for 5 years now. But my question is, Sites like jQuery, Bootstrap, Web Fonts, ... that provide free cdn for their products that webmasters can use thier cdn instead of just downloading their code and then use their own cdn.
What are the benefit for the providers of these libraries (seo wise,...) that they pay lots of money for the cdn and give it out for free?
Update: The reason I'm asking is that I have created a library and I want people to be able to download and use for free. I want to know what can I gain from providing free cdn for my library as many others do?