Because iPhones can stand alone as your all-purpose computing device. They are the centre of your digital life. They have all your photos and videos and other details.
The mac, therefore, does not have that role any more and the OS developers have understood that, but the hardware developers have not. They keep making hardware suited for that kind of user, but that kind of user isn't buying macs. They also aren't buying PC's, which is why PC sales have slumped for a while.
They keep developing the mac as if it's a hub for your digital life when in fact people use it as a workhorse. Compiling code including things like LaTeX for reports, doing various projects like audio and video editing, composing music etc., and gaming mainly, because a mobile device cannot do it effectively or maybe even at all.
The requirements for how much processing power you need for this depends on the application and the intensity with which it is used, but for games the game developer sets how much computing is needed, and almost no mac can keep up. Even the strongest mac laptop can barely keep up with a $400 PS4 Pro.
The PC allows you to do all that too as well as game, so given that why would you get a mac if you're a gamer? Maybe you prefer mac, but so what? That's how I feel.
If you don't game there is no compromise anyway and you can pick what you like, but many people both game and create, which is what Intel points out.
The irony of Intel's statement is that the reason their argument is correct has nothing to do with Intel. Intel is a dead weight in that regard. It's because of NVIDIA and Microsoft mainly.