I like this one, because you can really see the mangaka critiquing gated communities and gentrification. It is literally a run down area that was completely overhauled for luxury flats where the original residents aren't just pushed out but straight up obliterated to make space for ghosts (the rich).
In this case, it's a role reversal: the living residents are the rich people who were lured into the housing complex by promises of "utopia", and the ghosts were the poor people who died in the fire but seek to live again.
In the first chapter of this arc, they mentioned that "all the spots had already been filled." And in this chapter, they conclude with "With this, everyone's here". Basically, they needed to reach a 1:1 ratio between living residents and dead ghosts for total "resurrection" of the dead (number of spots = number of dead people). They succeeded at getting the exact number of people to sign up ("all spots were filled"), but then some of those people figured out what was going on and managed to hide until they were caught ("with this, everyone's here"). My guess is that signing up as a resident of Aoba makes you eligible for replacement because of conceptual/identity grey magic stuff, i.e., "You sign this contract stating that you live in this place where X person used to live; therefore, X person can be swapped with you."
Now that all the dead ghosts have come back to "life", the actual community is probably harmless now - there's no more dead ghosts to take the place of the living. They still might advertise if they just want more money, or they could sit on their laurels and celebrate their second chance at life (shame about what it took to get there though).
Edit
Motive: how did a bunch of dead ghosts construct the buildings in the first place? Why would the rich developer dude agree to this plan? Well, we see the Narrator have an affair with one of the residents (probably a former ghost herself). My guess is that he had a pre-existing relationship with her, but then she died in the fire. So he came up with this whole scheme for the purpose of bringing her back, regardless of how many innocents had to be sacrificed.