How challenging is it to add new libraries?
Another option is to get a library card at a library that does use Libby -- there are some that offer cards to non-residents solely so you can check out library books but idk exactly which ones
A niche thing which can affect stuff is some libraries only show their full catalog if you're logged in (and potentially which partner library you're a part of, if the library offers multiple). I don't remember if I just read this in their documentation or when scraping, found at least a few difference so logged in first