The iPhones getting their battery replaced are older iPhones owned by people who do not want to spend $1000 on a new phone. It’s people breathing new life into an iPhone 8, not someone debating dropping. $1300 on the latest release.

And those people also at one point spend $800 at least on a phone. Is $40 really a deal breaker?

I have an iPhone SE2, with 86% battery health, over 86GB of storage left and performance and size that is just perfect for me.

Why will I replace my phone if it's in just fine working condition and is sufficient for my needs, that too in just 4 years?

Battery replacement will work well for me once it's below 80%.

That’s just the point. Very few people who bought an iPhone are going to let a $40 increase in battery replacement costs deter them.