I mean, by the time your battery is in that state, you're well out of warranty. So they'd have to pay for the new batteries. I do agree with your key point tho

I mean, by the time your battery is in that state, you're well out of warranty. So they'd have to pay for the new batteries. I do agree with your key point though, but from a different perspective - they'd probably make more money from people upgrading their phones to the newest model.