As a technologist and a casual photog, I’ll chime in.
The answer is optics.
Previously, phones had basically one set focal point, and everything from a certain distance to infinity would be in focus. There was no way to adjust our change it, because the optics were basically sandwiched against the sensor.
More modern phones can do some level of focus, which allows focus to be set much closer to the phone. At first, this didn’t really introduce much thickness, and phones were fairly thick in the first place (at least, compared to today)… So it was merely a matter of shifting some things around to make everything work.
Now? Between the pulls for longer battery life, with the relatively stale battery technology in use (we haven’t seen any significant uplift in battery storage density in a while, some might be coming, but they’re not here - so the only way to add battery is to install a larger one); the push for thin/light phones, and the push for better image quality in phones (4k video, bigger zoom, bigger image sizes, etc)… Everything has culminated into adding space for optics, and making everything else slimmer. The only other area where the phone is growing in size, is the screen.
Personally, I don’t understand the race to be the thinnest phone. I don’t give a shit. I don’t want to be holding a piece of paper that makes calls. Back in the day, even the very chunky handsets of landline phones were not comfortable to hold for extended periods of time, and there were attachments you could get to make them bigger, so it would be more comfortable to hold the already massive (by today’s standards) handset against your shoulder. Ever seen someone try to hold a cellphone with their shoulder? It’s not comfortable.
… I know what they will say… Bluetooth! Headsets! (Blah blah blah). Handsets existed for landlines too. Nobody bought them. IMO, the only reason people use Bluetooth for calls is because they bought the BT headset for something else (like music). BT headsets for only calls were pretty much only purchased by the same dicks that bought headset landline phones.
Anyways, I’m off topic now. While I don’t get the compulsion to make phones thin, I understand that optics need space and it’s the reason why there’s a camera bump. Companies wanted thinner phones but needed space for optics, so this was the only way to accomplish both.
What if this lifetime is also a dream.
Like inception.