Sony solved open headphone jack while being water proof nearly a decade ago. The idea the phone can't have a headphone jack and be waterproof was a lie pushed by Apple to save money on not having to put in a headphone jack.
I've been using Sony phones in the shower and at the beach for years now and only briefly switched to a different company when they tried to pull that headphone jack removal of crap briefly when I needed a new phone.
My understanding was that it’s always been about the physical size and the impact it has on the stack-up of iPhone components. Looking at a standard mini-jack vs. my iPhone 13, the connector itself is close to 40% of the thickness of the phone. Add the additional size for the jack’s structure and you quickly get to a point where the phone has to be thicker.
Now, has Apple gotten too obsessive about thin phones? Maybe - but that’s a different discussion.
If that is the case, I have a hard time believing it's still true on any model past iPhone X. There's plenty of space to fit a 3.5mm jack in there, I would happily trade any/all of the FaceID hardware or Lidar components for a headphone connector.
I don't see how that could be true. The thinnest ever iPhone was the 6, and it had a headphone jack. The phones since then have been 3-20% thicker.
Some searching suggests that 5mm is about the point where it won't fit, and iPhones are comfortably 7+. One of these phones is 5.6mm thick with a headphone jack and has near-zero bezels.
I've been using Sony phones in the shower and at the beach for years now and only briefly switched to a different company when they tried to pull that headphone jack removal of crap briefly when I needed a new phone.