That's true, but it's not a sufficient argument. An integrated MiniDisc player would also not stop you from playing music from files stored on the phone, but it wouldn't be a strong argument for including an integrated MiniDisc player.
The real argument is that having a wired option is not a money maker for apple. Apple wants YOU to buy accessories, which are the meat of their business with ridiculous margins. That's just selling to users something they don't need in the first place and making them pay premium for it.
What is that an argument for? It seems like you should be arguing why removing the jack is a bad idea, but plenty of good ideas could also be implemented purely to make money.
Apple will likely sell tens of millions of AirPods this year. At $159 each, and presumably at very healthy margins.
This is no small business, even by Apple's standards!
Removing the headphone jack was a marketing-driven decision. AirPods are a cool product, but wouldn't have sold anywhere near as well without the forcing effect of the jack removal.
This guy managed to install a fully-functioning jack back into an iPhone 7:
How many fewer AirPods do you think they would sell of the iPhone 7 still had a headphone jack? Given that every iphone 7 came with lightning EarPods and a lightning to headphone jack adapter, I would guess that AirPods sales would barely have been affected.
