> I don't know about tumblr, but reddit doesn't allow nsfw subs out of the box on mobile, and for logged in users, you have to explicitly enable it.

This is an Apple rule. From the App Store Review Guidelines:

> If your app includes user-generated content from a web-based service, it may display incidental mature “NSFW” content, provided that the content is hidden by default and only displayed when the user turns it on via your website.

— https://developer.apple.com/app-store/review/guidelines/#use...