[DrillBIT]

In Garo season 1 it took place in a big city. Normally you would think it is something similiar to the modern world like ours.
But then in Garo SP the introduction of villiages (and hinting there are more of those out there) and the makai priests community (which is much larger than you think). It seems it is not that modern after all.
In Garo season 2 the introduction of the council and the makai knight (and priests) population makes me think that these modern citics are pretty much "satellite shelters". The council are protecting these places and the normal people in these zones.

In TOWSITD it goes beyond that by saying a private incorporated foundation can actually buy out a single shelter, and has its own guardian forces.

The world doesn't change much when everything is stale. You might see some improvement in lifestyle, but overall nothing has changed.

Also the mystery of the map of Volcity and the map of the Promised Ground.
Amemiya said it was done on purpose, but no more than that. I guess it plays a big part on how that world actually works.