Apple like to play dirty in the business world but they do not like it when the table are turned and it is them on the receiving end. Take the app store for example. Apple designed it, built it, own it and thus do as they wish with it. Anyone that want's to use the app store is basically told 'You do it our way, you do it how we tell you, when we tell you and price it how ever we want' and if you do not like those terms you are free to go elsewhere' and many agree with Apple on these, even the courts agree with Apple on this but when companies do the same to Apple, oh hell there be fireworks. Apple like to treat others like dirt but when the tables are turned on them it's a whole different story.
Apple wanted to move away from PPC chips and the best around at the time was Intel (they was far superior to AMD at the time). Intel, within reason could demand what they wanted because otherwise Apple would have no CPU chip. I have no doubt the continued arrangement with Intel to use their CPU's annoyed Apple very much because Apple could not hold all the cards to get what they wanted. Intel could have pulled out at any time and Apple would have been in serious trouble, no CPU, no computers and they would not have time to use a rival CPU maker. Apple finally got away from Intel's clutches by making their own CPU and of course what do we see, Apple royally dumping Intel's ass. Qualcomm are in the same position as Intel were, they are in control because without Qualcomm modem chips, Apple devices are a poor version of themselves. So what is Apple trying to do, get rid of Qualcomm's control by developing their own modem chip.
Remember the TV series Dallas, Dynasty and Falcon Crest? All about one family wanting control and domination the business they were in and destroying anyone and everyone that got in their way. Well that is Apple, they want to be in control and dominate over others. They design and build their own computers and mobile phones and thus they do not want to have to rely on others for major parts of their machines in this case the CPU's and modems. One of those hurdles is gone, Intel because now Apple make their own CPU. Now they need to remove the other hurdle, the communication chip which would stop Apple's reliance on Qualcomm. Qualcomm can set it's own terms and conditions and prices of it's modems and if Apple don't like it Qualcomm can quite happily walk away. You see, Qualcomm is in control, not Apple and Apple wont like this, hence their long continued effort into developing their own modem chip.
Remember, with the app store Apple can say 'it's our way or the highway', Intel used to be able to say this but not anymore due to Apple making it's own CPU. Qualcomm still have the power to say to Apple 'it's our way or the highway' and Apple do not like this. As i said, Apple is happy to do it to others but do not like it when it is done to them.