That’s Lee Muhan, was he called? Like the main entity, who the three Mugos were before enduring the abuse needed to turn them into a fake god. Only thing is, he is like the past, like who he was, so combining the three of them now would most likely result in a whole different Lee Muhan, I guess. Also, remember that Lee Muhan was completely obsessed with the mc, because of their past life together most likely ┑( ̄Д  ̄)┍
I think you are also somewhat right, cuz it would make sense to think that all of them do not want to be combined again (two of them want to NOW that they share mc in common, the other one doesn’t want to because of his divine delusions, let’s say) and it seems like he is the only one who knows more about the whole situation than he is letting on, based on what we’ve seen so far (when their mind is depicted as a staircase and on the bottom of the floor there is this unsettling figure, lord Mugo lowkey noticing something weird and telling the other monster Mugo, a panel in a chapter where Lee Muhan is screaming nonsense, all the early peeks we got at what happened to Jahyeon in his past life, etc…). I remember all these details cuz IM SO INVESTED WITH THIS STORY WTH ITS SO GOOD, ALSO, yw bestie, anytime ٩(๑❛ᴗ❛๑)۶ <33

Ummmmmmmmm who da f is that