I believe in some cases (e.g. instagram) the user agreement you sign when using the site makes your copyright over e.g. the pictures you upload be handed over to the site owners (again, to prevent competition). Just to point out that the common sense idea that "you own the data" thing isn't always true. Nevertheless this question has been resolved through other comments on here so it seems not to be the case in this scenario.
It would probably be illegal to crawl Goodreads, if that’s what you’re thinking about?