Because viewing/storing this material is illegal for everyone except the minor in question. If a minor posts a nude picture on Reddit and I view/save it, I'm guilty of possession of child pornography. Maybe I could get the charges dropped if I can argue/prove I didn't know they were underage, but lives are ruined over mere allegations of child sexual misconduct and that reputation would follow me everywhere.
>There's really no way to prevent this but to abandon privacy/force verification.
Which is why official producers of pornography are required by law to verify age and consent of all of their actors (18 U.S.C. § 2257). The problem is when they allow producers to distribute pornographic materials on their platform without verification that the producer is following the law, like PornHub and Reddit and Imgur and Tumblr etc. Forcing verification is already in the law for producing pornographic materials.
>It's not a problem exclusive to pornhub
Correct, but the fact that other companies are violating the law does not absolve PornHub of their responsibilities.