If you've ever done it, you will quickly realize that it's obviously been designed as a non-replaceable item. It's a unnecessarily delicate operation, just to replace a battery!
Any Apple Store will replace the battery in any Apple device for you, at the cost of the new battery.
Theyre not designed to be user replaceable, no. They also don't need the extra packaging and associated cruft that user replaceable batteries have, so they can be shaped to fit device shapes, and sized to give maximum charge capacity.
Lol, the person who I did it for (this was a while ago) was told $150 to replace the battery in her old iphone. I bought a battery on ebay for $5, delivered from China, including the tools I needed, and did it for her.
It was nerve wracking, quite delicate and fiddly and easy to break something. The first time I forgot to reconnect the tiny microphone flex cable so I had to open it up again to reconnect it, but I got there in the end. She was very happy but I wouldn't do it again for someone.
TLDR: quoted $150 at Apple store, did it for $5 and about 30 minutes of hassle. Apple is a planned obsolescence scam.
Theyre not designed to be user replaceable, no. They also don't need the extra packaging and associated cruft that user replaceable batteries have, so they can be shaped to fit device shapes, and sized to give maximum charge capacity.