I think it’s exactly what @HerdingSnails@lemmings.world said. I assumed it was some kind of dodgy spam at first until I checked your post history. It’s definitely off-putting for users linking from a NSFW tagged post straight to another website with an NSFW pop-up, and a login prompt. Very few people would go to the bother of creating an account just to see unknown content, so I’d guess that’s the main problem with it.