Even though Lightning is capable of dynamic signal assignment and could supply analogue audio over the port, it's unlikely because it would have to be backward compatible with all Lightning ports which may conflict with other devices. Moreover, I believe this move is intended to drive wireless adoption, and to a lesser extent digital wired solutions. If Apple offers a cheap analogue solution, then customers will have to use an adapter without necessarily getting any other benefits. Pushing the DAC onto the headphones means Apple is relieved of the responsibility of anything but supplying a quality digital signal true to the file source, and gives everyone a reason to move toward wireless and digital, which they otherwise wouldn't do if they can get a cheap adapter for a lot less.
Because Apple doesn't want customers buying a desktop peripheral and plugging it into their iPhone complaining that it doesn't work, or worse causing damage. Likewise plugging Apple iOS peripherals into a PC. Also, USB-C is not yet a standard, and even if it becomes one, who knows how long it will be a round. It also takes up considerably more internal space than the Lightning connector.
That clears it up. But merely running digital audio through the headphone jack just creates more redundancy, since digital audio can already be run through Lightning as it is. The reason I said there needed to be 9 poles is to accomplish the functions of Lightning via the headphone jack (Lightning has 9 conductors), which is why I specifically mentioned the iPod Shuffle which has 4 poles (tip/two rings/sleeve) which acts as a USB-A connector.
Apple is trying to reclaim over 240 cubic mm of space inside the phone from a redundant port that only provides one function. And yes, betray is one possible reason for reclaiming that space. But also new features, without making the phone larger. Every generation is a dance that shrinks the existing components, improves efficiency of the existing battery, and removes redundant processes. They're trying to hit a particular design sweet spot that maximizes the size of the phone for as many customers in as few models as possible, a strategy which has what has arguably made Apple so successful since Steve Jobs returned.
You don't have to agree with it, but there's valid strategy behind it. In fact as I've said before, I'll bet the competition would love to eliminate the 3.5mm jack for the very same reasons, they just don't have the balls or loyal fan base to do it.
