Adapters are always less than ideal. People don't want to have to use completely unnecessary accessories with their phones just so they can listen to tunes at the gym or on the train with the expensive headphones they already own. It's just another thing to lose, break, and keep track of as well.
It's not the same as the move to USB-C because USB-C phones all have headphone jacks still, and many of them have wireless charging as a second option, as well as quick charging.