You’re coming at this from the angle that the headphones are just going to be used with the phone. Why should the headphones I use for my desktop amp, digital drum set, music work, etc all change to support my phone?
I get for the vast majority of people they use headphones with their phones and that’s why this was allowed to happen, but in music the overwhelming majority of headphones use the standard jack and I can tell you there is no way in hell that is changing any time soon. People pay a lot of money for audio equipment and they’re not throwing it out to use the crappy DAC built into headphones.
Is this niche? Sure. But it’s a standard that has worked and will continue to work forever due to its simplicity. The analogue headphone jack will long outlive USB-C, mark my words.