Well for the case of "nicer libraries" I suppose I mean high quality libraries. Also good to note that I am referring to libraries in the web development/backend sphere here. I have a hard time thinking of some real world examples of there being a larger quantity of quality libraries for ruby, it's more a feeling that I get.
Around documentation and usage I think it comes down to the fact that for Python libraries a google search usually takes you to the modules page on the PyPi registry, to a project website or a read the docs instance. I usually find that where ever I end up doesn't provide all the information I want, e.g what's the latest version, what are some typical use cases for this library. As a concrete example let's compare Flask and Sinatra.
For both Flask and Sinatra a google search gives me their respective websites as the top relevant result. In this case I find both websites don't really provide all the information I am after. When I navigate to their GitHub page however the difference is more stark. Sinatra uses GitHub flavoured markdown to render a nice guide with increasingly more complex use cases. Flask just has some non markdown text pointing me in a few different directions. I could probably find all the information I need to setup and use Sinatra from just the GitHub Readme whereas for Flask I'd have to go navigate their read the docs page where all the documentation and usage instructions are spread over multiple pages and sub pages. I guess it comes down to my preference for the more concise format of a long markdown README.md vs the experience with a read the docs like set of pages.
I recon this is a bit rambling, it's kinda hard to put into words what my feelings around this are and why I hold the opinions I do.