Yes, even Okumura-san found it worrisome. If I had to hazard a guess, the key difference may be what Akira described- when Maruki reached the height of his power.

[Hmm... come to think of it, maybe there is something to it.

Akechi takes a sip from his second drink, then carefully sets the glass down.]

This is purely hypothetical, but perhaps Maruki's presence at Shujin is key. Ren and I have established confidant bonds with him back in our world, and Ren has been trying to help him with his "research," though I suspect that is solely a front, if he truly is our brainwashing culprit.

But if Maruki is a cognitive psientist, regardless of world, it is possible he could learn of Mementos. And I was informed that this false god lurked at the very depths of Mementos. But the god was defeated, so perhaps...

[Hm, but does that make sense? Or is it, perhaps, a stretch to assume?]