It is well known that Apple is getting a lot out of third-party manufacturers that pay for a license to sell Lightning-type accessories, so it is not surprising at all that the company has found a way to continue doing this even after upgrading the iPhone with USB-C. Of course, this approach also helps with avoiding damage from potentially dangerous and unknown peripheral devices, but this could very well be achieved without such harsh limitations.
Something else that is worth noting here, is that prolific Apple analyst Ming-Chi Kuo, who is often correct about his predictions regarding the company, has stated that there is a good possibility Apple would reserve the USB-C perks only for the iPhone 15 Pro and 15 Pro Max. This would essentially leave the two more affordable iPhones with the same capabilities as the Lightning port offered on the iPhone 14 series.
In other words, we could see the same approach Apple took with the entry-level iPad and iPad Pro, where the cheaper model could only go to 480Mbps, while the pricier iterations could reach speeds of up to 40 Gbps — an ocean of difference between the two.
