Earlier quoted context omitted.
This phone was designed, locked in place, and started manufacturing years ago.
Adding a fingerprint scanner doesn't affect every component in the phone. It doesn't affect the display, CPU, dimensions or anything with a long lead time. It affects the power button. Apple had well enough time to add it.
I would give them some benefit of the doubt to one of the biggest companies in the world that they had at least a dozen people research this and came to the conclusion that they couldn’t or didn’t want to (due to cost, design, etc).