@rose I hate to "um, actually" on this one but the theortical issue is that cameras can extend outwards off the mainboard. A headphone jack can't, and you need room for it inside the phone in-plane with the board which means less total component space.
I mean it's all moot anyways, the real reason they say that is because Apple said it, and Apple said it because either they wanted to push AirPods, or they felt that wires ruined the brand and image of their device (like with the magic mouse) and so invented an excuse for removing it, pick your favorite.