Thinner, lighter, faster
John Gruber, on the "thinner, lighter faster" Galaxy Book S compared to the MacBook Air:
Well, there’s the small notion of, you know, the operating system. And let’s see if it really does get 25 hours of video playback. But the point stands. A lot of people using MacBooks today aren’t devoted to the MacOS experience, and might switch, based on hardware alone. The ARM revolution for notebook PCs is coming, whether Apple is ready or not.
John's right that a large chunk of people using MacBooks today aren't devoted to macOS. But... macOS also just isn't as good as it used to be. That's not about software quality, something that bothers technical users more than ordinary ones. It's just that Windows 10 has got better, to such a degree that unless you're bought into the whole Apple eco-system there's not much point in going for a Mac.
The Mac is now Apple's weakest link.