I don't need to be able to swap a spare battery like we did 15 years ago.

However when your battery is old, and drains fast, it's really nice to be able to order a new one and easily change it by removing 4 screws.

Not having to perform surgery on your phone, heating it to remove glue, etc.

I'll never forget the feeling when you get an old phone, replace the battery and it's like brand new again. People no longer need to replace their phone every year anymore so being able to just replace the screen and battery makes the device practically brand new.

I wouldn't want to design the phone around an event that happens every 3 years at minimum.

Sure, but so far I've replaced my phone screen once and the battery never, I suppose both would be equally easy though. Why is heating a big issue but removing screws not? Shouldn't we mandate user-replaceable screens too? Soon you'll end up regulating all phones to be modular.