for the same reasons I don't use wireless mice or keyboards.
If the battery is replaceable, then you have to keep batteries on hand for when they die. ( which is constantly and at the worst possible moment )
If not replaceable, you get to keep buying new mice and keyboards every few years when the batteries ultimately give out.
In your phone, the battery is likely going to be the first component that dies taking the whole device with it. Being non-user replaceable, this forces you to upgrade to the next phone. It's nothing more than planned obsolesence. Same thing for the wireless, battery powered headphones you'll be using soon.
I have to replace my headphones soon not because the battery died, but because I've worn out the ear cushions.
Considering I've used them for at least a DECADE, I'm pretty sure I've got my moneys worth from them.
Then again, I may just try to replace the ear cushions myself and keep on using them until they truly die.
New hotness is not always better.