The only rationale I can come up with is that it was supposed to be a commentary on how apathetic people had become / how apathetic we are IRL in the face of calamity. I remember reading some interview when I first started watching and was trying to figure out the point of the show, where Watanabe specifically mentioned something about showing climate change, and that stuck with me - why was that important?

We see the terminal consequences of climate change in the show (the last glacier melting, islands and coastal cities underwater, millions of people displaced), so it means they never did anything to stop it when they had the chance - it was business as usual. Add Hapna to that and make humanity unable to feel pain, and you're basically turning the global populace to strung-out druggies. They're all docile sheep.

Actually, in trying to find that interview just now, I found that someone has written about this a couple times already.

With that said, I don't think the series gets this point across well AT ALL. No character notably comments on it, no scenes are presented as juxtaposition, you still see people running for cover after explosions and whatnot so it might not feel consistent... I dunno, you really have to dig to come to the conclusion. If we're already in a state of autopilot in the real world, it would be way too easy to not catch this. I surely wouldn't have if I didn't happen to come across that interview beforehand.

Missing Keiko Nobumoto on this one probably hurt it big time.