I think wired devices are becoming obsolete. It's the last of old tech to go isn't it? Besides complete audiophiles or people that can have their phone sitting right next to them while they work, most people use bluetooth now. I'd rather see that space for better water protection or some other type of tech I may use ..bigger battery, better speaker ....
Bluetooth is allowed on flights just fine. As well as Wi-Fi. Only cellular has to be disabled, and even that is a gimmick and a lot of people don't use the airplane mode anyway, and we're all still fine.
We could be speculating all day about it, but does "why"really matter? It's not coming back. And it's pretty much guaranteed it will be gone from the S11 generation as well. I was upset a little at first too, but after using the phone for over two weeks, it was actually really easy to adjust. Yes I had to buy an adapter, it cost me $9 at Best Buy. I use it in a car, and my wireless Galaxy Buds for earphones. The sound with the USB-C adapter is actually better, it's clear and loud and has better bass. And wireless headphones are just so convenient, it is the way to do it in 2019. We might as well start embracing it.