Because you’re not just paying for a physical device. You’re also paying for the software that runs on it which is best in class. And before people start saying it’s not, how many people are running 7 year old androids compared to iPhones? In USD, A brand new iPhone, kept for 7 years works out at 32 cents a day - phenomenally cheap for something integral to modern day life. And that’s not even taking into account you can most likely sell it for $50/$100 at the end of that seven years, making it even cheaper.
I changed the battery last year, it costed me 13$ (~12 euros), it is as good as new.
Now it might be that my Android phone is Chinese as well, so it actually costed me less than 10¢ a day. Even if I had to replace my Android smartphone, I could have changed it 3 times in the past 7 years and still spend less than buying an iPhone that lasted me 7 years.
I could still easily sell it for 30-40 euros, making it even cheaper.
So you've edited your comment to bring up slave labour for some reason, so obviously your Android phone and your $13 battery are all ethically sourced right?