I've read half of these comments and skimmed the other half and have seen no one offer a reason (aside from Apple sucks) that the non-Pro will be limited to USB 2.0 speeds. But there is one, I think.
We expect from rumors that the iPhone 15 is going to feature the same processor as the 14 Pro. The 14 Pro is Lightning and couldn't use speeds over USB 2.0, so it's probably just a USB 2.0 controller built into the silicon or package. To save money, Apple is going to re-use the the same silicon in the iPhone 15 and it will then be 2.0 speeds. For the same reason, the new USB-c iPad is 2.0 speeds. So far the Mx based chips are the only Apple Silicon that supports faster speeds.
Expect the 15 Pro to get 3.0 or TB speeds and that to trickle down to the non-Pro iPhone 16 in 2024. Annoying, but understandable.