ChatGPT is full of sensitive private information and spits out verbatim text from CNN, Goodreads, WordPress blogs, fandom wikis, Terms of Service agreements, Stack Overflow source code, Wikipedia pages, news blogs, random internet comments, and much more.
We don’t, but from what I’ve seen in the past, those sort of forums either require registration or payment to access the data, and/or some special means to download it (eg: bittorrent link, often hidden behind a URL forwarders + captchas so that the uploader can earn some bucks). A simple web crawler wouldn’t be able to access such data.