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.
Oh damn. Autocomplete + tiredness for the win I guess :p