For the headphone jack, it was about establishing Apple products as high-end products for fashionable people who can afford to buy accessories like AirPods
That might have been one of the goals but I doubt it was the only goal. Another reason for removing the headphone jack is dust and moisture ingress protection. It's difficult to achieve an IP67 rating in a phone with a 3.5mm TRS jack. This is due to the shape of the connector and the extra thickness you need to add to accommodate a jack with sealing rings. By switching to the lightning connector exclusively, Apple was able to achieve IP67 ratings in all their phones after the change.
This is a huge improvement for users because previously a lot of phones were being brought in for service showing liquid damage. Having your phone die due to dropping it in some water is a terrible experience that is now quite rare due to the IP67/IP68 ratings of modern phones.
Yes, you're right, there are technical benefits too.
Still, I think the primary reason Apple felt comfortable dropping the headphone jack while contemporary Android phone vendors didn't, was that Apple could afford to lose customers who didn't want to upgrade to AirPods or other Bluetooth headphones. What they lost in direct sales they would regain in brand reputation. That was about market positioning, not about engineering.
By the way, I just looked up some specs and my unfashionable Samsung Galaxy A52s with a headphone jack also has an IP67 rating, and it is the same thickness as Samsung's current flagship model, Galaxy S23, which doesn't have a headphone jack. Both devices are only 0.6 mm (7%) thicker than Apple's current flagship iPhone 15. So while I'm sure adding a headphone port incurs some engineering cost, I feel like this cost isn't insurmountably high, and it's not true that you can't have IP67 and a headphone jack at the same time.
That might have been one of the goals but I doubt it was the only goal. Another reason for removing the headphone jack is dust and moisture ingress protection. It's difficult to achieve an IP67 rating in a phone with a 3.5mm TRS jack. This is due to the shape of the connector and the extra thickness you need to add to accommodate a jack with sealing rings. By switching to the lightning connector exclusively, Apple was able to achieve IP67 ratings in all their phones after the change.
This is a huge improvement for users because previously a lot of phones were being brought in for service showing liquid damage. Having your phone die due to dropping it in some water is a terrible experience that is now quite rare due to the IP67/IP68 ratings of modern phones.