One should be at the bottom one at the top. I understand space on the phone is a premium but a second port would make the phone so much more usable. Wired headphones, flash drives, camera modules, speaker modules, keyboards, even connection to a TV, all could be used while charging. It's a shame it's not a thing, USB is extremely versatile port, but you only get one and it's used for charging half of the time. (I am aware dongles exist)
I honestly don't think it made a noticeable difference in terms of selling AirPods, it simply reduced cost.
I only buy phones with 3.5mm jacks on principle, and yet I stilled jumped at the chance to get Pixel Buds cheaper when I got my 5a because of how convenient they are. The decision between wired and wireless is now nearly exclusively because you prefer either fidelity or convenience over the other. Not whether or not your phone supports them. Besides, if you're picking fidelity you probably scrutinize much more on a phone than headphone jack or not.