I totally disagree with you on Apple doing "nothing." I would also disagree with the other extreme of saying it's all about Apple, with the reality somewhere in the middle.
1) Apple started designing its own chips and ditched x86. Apple's architectures have proven to be very competitive. (Side note: A lot of Apple's top chip designers are ex-Intel people that left in the Krzanich era — often forced out the door because they were older white men. This caused a lot of problems with moving beyond 14nm, needless to say.)
2) Apple's iPhone was a revelation to the smartphone world, literally. Pre-iPhone cell phones were flip phones with keypads and tiny screens iPhone changed all that, the rest of the industry had to play catchup. There are millions of people that only have a work laptop, and at home all they really need is a cell phone, maybe a tablet.
3) Intel totally failed to capture any part of the smartphone market, in part because of points one and two. ARM SOCs were good enough for the first four iPhones, but when Apple rolled their own architecture it got the advantage of full hardware and software control. I don't love Apple, at all, but credit where it's due: The company has rocked the smartphone market, and leveraged that to expand in other areas.
4) Because if its success, Apple was able to charge a premium for its new phones, and in turn pay a premium to TSMC to get first access to the latest process nodes. First N7, first N5, first N4, N3, etc. All the billions funneling into TSMC via Apple cannot be understated. It was very much a win-win scenario.
5) People used to upgrade their PCs every few years. Now, people upgrade their smartphones every couple of years. And smartphones often cost $600–$1000. And they roll that into contract pricing so it feels less painful. I have family and friends that always seem to have the latest model iPhone who balk when I tell them it's time to put their eight years old laptop out to pasture and buy a new $500 model from Costco.
Apple didn't carve out a massive slice of the desktop/laptop market, no. It's still less than 10% and probably will remain so for a long time. Or maybe some other device and company rises to the top. But iPads have reached the point where they're viable laptop alternatives, and if you count those the percentage of "laptop" users that Apple has taken from Intel is far from trivial. Tens of millions I'd say.
And it's obviously not solely Apple doing this. I'm not trying to imply that at all. But it's equally disingenuous to postulate that Apple did "nothing" that has hurt Intel. It played a part is what I'm saying. Bring in all the mobile SOC companies like Samsung, Qualcomm, MediaTek, etc. and you have a rather sizeable chunk of the world's computing market that's not doing anything directly to "help" Intel (or AMD or Nvidia).
I
sort of predicted this eight years ago while at PC Gamer (or Maximum PC, which became part of PC Gamer). Except I saw it mostly as a threat to Microsoft, which weathered the storm just fine thanks to data center stuff. But in the comments you'll note that I'm also discussing out Intel and PCs are equally at risk due to a paradigm shift in how we use computing.
Intel is in serious jeopardy right now. If it starts selling off chunks like AMD did with GloFo, that could very well be the end of Intel as we knew it. I suspect the US government would step in and take over before letting that happen, but then governements aren't good at being efficient. What Intel could do with $10 billion of gov't support, the government will do on its own with $100 billion.