It would have been a lot more powerful if, once a world or an area vanished, to have it erased completely from history, like it had never existed at all.
I guess it's to reinforce the cruelty of merging worlds events.
Seeing this man in Salsabil crying for his forgotten wife is sad and cruel. Same goes for Nhazu who is feeling than Dogha is a good man but seeing than all other Tehah citizen despise him.
Hotupa, when allies meet Shams after the destruction of Janam, raises hard to answer problematics : Should we reveal the truth to Shams and his grandparents or not ? Hotupa's advice is "What you don't know doesn't hurt you." It's maybe true in this case if memories would have been completely erased and modified.
But since we have this feeling than old memories are suppressed and still linger in subconscious, it's probably more cruel to let people in this unsteady state.
By the way, it's pretty weird to see that Seig decides to reveal the truth to Shams, but not the grandparents... Oh well, he doesn't care about them, he doesn't need them as star bearers...