For some reason, many Python libraries use readthedocs.io, their documentation is sparse, very shallow and the API reference is left undocumented, that I'm usually displeased whenever I see that website and colour scheme. I know that I'm gonna be left wanting. Conversely, the Elixir documentation is so high quality that I'm put in a good mood whenever I land on their version of the documentation browser (generated by ExDoc).

It's not the fault of readthedocs per se, I guess it's what most projects that want a barebones documentation site and call it a day use.