Hoarding porn is kind of useless nowadays, especially without any kind of selection and categorization, but maybe someone does it because it's their hobby (or obsession), who knows.

Also if a lot of people has a bunch of porn images scraped from forums it's quite possible that eventually some of that might become illegal as the laws change here or there around the world. Should they proactively delete everything? Sure, they could. To be safe.

But this kind of safety is absolutely the bad kind on the long term. (Though of course it's possible to advocate for reform while not storing content with uncertain legality.)