> Apple wasn't required to use USB-C up until the iPhone 17 release in September 2025

No, starting December 28, 2024 they could no longer import and sell iPhones with Lightning ports, so they had to at the very least make the iPhone 16 in September 2024 USB-C.

But Apple likes to sell the previous model phone as "the cheap option", so to have a previous generation to keep selling they had to add USB-C a model year early.

Apple added USB-C to the iPhone as late as they possibly could with their typical product cycle.