(Warning this is just my opinion)
1. Apple wanted more internal space,due to the dual cameras and the taptic engine
2. Going wireless and convince people to spend money on thier stupid air pods
3 beats..... Beats use the new w1 chip which makes them way more convinient and generates more cash
4.licensing.....apple can sell thier w1 cips (and make it so called "made for iphones") eating into the profits of other manufactures ..giving beats more money for celebrity endorsement,in turn increasing sales
basically to sum it up its crazy business strat and apple knows its gonna work cause there are so many apple fan boys who belives apple blindly
i would like to know your opinion on "why apple killed the headphone jack"