If dooshka was banned for the MM my guess is that someone wrote a convincing complaint to Sony about him. I'm not going to claim I've actually read and memorized the EULA from Sony so this is all hypothetical on my end. If someone has read it, feel free to call me out on it too.
Any time you need to be signed in to your PSN to use something (like Dark Souls online play) you're under the Sony EULA. There's a lot of rules in there but they're all about "fair play" and "fair use" (generally an EULA is, again I don't have Sony's memorized). So regarding the MM, From decided that the save backup feature would be locked. By using the MM, you're bypassing this game restriction. Well, the original person did at least. Using it is at the very least a promotion of someone else's likely breach. It's very well possible that Sony considers this an "unfair play" or "unsafe use." Without the EULA in front of me I'd be hard pressed to say what clause they would cite but there could be something ambiguous enough to justify their ban. In my opinion it's kind of a reach but without knowing the EULA by heart who knows what's in their terms that they're using as a basis for this ban. Another option is that they somehow discovered or inferred that dooshka had trophies he didn't earn. Again, it's a nitpicky thing but it's possible and would be proof of improper usage. And the MM does result in unearned trophies.
My best guess is that somewhere in the EULA there's a clause that's (paraphrasing here) something like "don't modify things." They're likely ambiguous and meant to capture a large variety of actions so that Sony can do something if there's a problem. Usually nothing is done however. While the MM isn't a hardware modification and only a mirror of someone else's modification of the coding they could still likely justify a ban under an ambiguous "don't modify" clause. I am still imagining that someone wrote a pretty convincing complaint to them though as they would need to check into the account a little before banning.