I came here to post something similar. PG is perhaps still important as an archive of proofread OCRed public-domain material, but for ordinary people, the shadow libraries have vastly more stuff. After all, readers don’t want their reading to be limited to what was published before a copyright cutoff date many decades ago.
Well, mainly in the fact that Anna's has several orders of magnitude more books, and includes research publications and more, ah, contemporary materials to boot.