Never had that problem. I'm certainly not going to preemptively switch from iPhone to Android - which has a laundry list of its own problems far larger than the lack of a headphone jack - in order to avoid an issue that may or may not occur with a function that isn't one of my primary use cases in the first place.
I have a pair of headphones I like that can connect via bluetooth or wire. I have a headphone dongle that works even if it is a minor inconvenience. I also have the cheap lightning headphones that came with the phone.
Basically, the headphone jack issue has been mitigated to the point where it's simply not an issue for a lot of people. Maybe it costs Apple a sale here and there. I would be willing to bet a significant number of buyers don't realize it's missing and an even larger number don't care enough to make an issue out of it.
The headphone jack issue is old news anyway. It's been multiple iterations that haven't had it and some of them sold well. It has absolutely no bearing on sales of current models.