This fallacy seems to be common in discussions of Apple. Apple is very profitable, therefore everything they do is infallible and impossible to improve.
Look at a picture of an Openmoko device. Just look at it. Here:
https://en.wikipedia.org/wiki/Openmoko
Compare this to various modern phones with a replaceable battery:
https://www.androidauthority.com/best-android-phones-removab...
There are obvious reasons to expect the former to fail in the market but not the latter, even though they all have a replaceable battery.
Meanwhile the Apple devices further run iOS and are compatible with iMessage and the complete set of third party iOS apps, which are a large component of their success, but none of which would be any less true if they had a replaceable battery.
Doing a lot of things right can't prove that they're not doing a specific thing wrong.
Rather, they are iterating upon the same few products with a zillion engineers in eensy weensy form factors where space is at a premium, so they probably think about why they do things a certain way.
There is a good reason, and the reason is that Apple doesn't want people to easily repair their phones.
There is an esthetic consideration in that they won't be able to use a glass back, but that's seriously minor. They can put paint and gloss on top of ceramic or tons of other solutions for just a bit more cost.
I'd bet a lot that the primary reason they did this was to make the device a fraction of a millimetre thinner; Apple seems to obsessed with thinness at the cost of everything else.
Personally, I'd much prefer an ever-so-slightly thicker phone with a removable battery, and I rather doubt I'm alone in that.
This is hardware engineering, and high quality engineering at that. When Apple decided to use an adhesive rather than screws they could would have had excellent consideration of cost/quality/aesthetic issues.
It is true that they could easily create devices to match the requirements of randoms on Hacker News, but that isn't going to lead to Apple - the once in a decade consumer products behemoth. It leads to the Openmoko. Turns out nearly nobody wants that.
So yeah, it is an "All Apple would have to do", but evidence is Apple is much better at deciding what it should and shouldn't do than back-seat designers. Sorry if that sounds a bit brusque, a nerve might have been hit here. But hardware isn't easy.