Other people in the comments have pretty much covered it already, but in a nutshell;
The page was not uncensored, it had pornographic material added to it by the scanlator.
MD has Pornographic content deliberately filtered out for guests (completely) and for users by default, and allowing pornographic content to exist in Erotica-tagged works has gotten us banned in multiple countries before.
Editing in pornographic content that does not exist in the raws either makes us serve pornographic content to guests (putting the website at risk in multiple countries) or requires to raise the content rating of the entire work (which would be inaccurate, and lock many people out of reading it, over the actions of one user) - neither of these are acceptable solutions.
Thanks, BraveDude. That's very helpful to know about.
Just a follow up question, though, so I can be sure that Akatsuki isn't really justified in a bid for "independence from MD". (I mean, yeah, sure man. Go ahead. But I sure as fuck wouldn't want to trouble myself over everything needed to run a website to host manga if there's a perfectly good one already that does it all for free.)
Would it have been permitted if Akatsuki had started another version of this title? I mean, like when some groups do colorized versions of a title. Only instead, this would have been a "fan edit" (and indicated as such in the title and in the tags) to include the pornographic content, and be rated appropriately so it would not accidentally show up for a guest or a user who has porn filtered by default. Would that have been fine?