Macs have a certain set of features which is not even close to being matched by any other laptop, as far as I'm aware. Not everyone values these features, and for them, the Mac is just overpriced.
- solid and beautiful chassis, no plastic-y uninspired 2008-Dell design here.
- large, beautiful, high-DPI screen looks great and has crisp text. You can seamless rescale the UI to get effectively a 17" resolution or 13", depending on how big you want your UI elements to be.
- the trackpad feels fantastic to your fingers! Two-finger scrolling through a document is so natural and ergonomic. Whenever I use the stupid Windows mouse wheel, it's either 3 lines at once, which is not enough, or one page at a time, which is way too much; I've never used a Windows laptop with a trackpad, I hope scrolling on that doesn't work like the mouse wheel.
- macOS is a Unix that works. Sleep works out of the box, every time. Wifi works, and connects instantly when you open the lid. After configuring the settings on first install, I basically never do sysadmin again for the life of that version of the OS. (I re-install from scratch when I upgrade; I know the happy path will work, but as a software developer, I know upgrading has all kinds of edge cases)
- macOS has a very consistent look and feel, and looks elegant. It also has all sorts of little details that go practically unnoticed but add up to a better experience.
For non-technical users:
- there is an Apple store within about 2 hours where you can talk to a live person, try out the machine in person, etc. which makes you feel secure.
- I have had exactly one macOS tech support request in over ten years (some girl did not know how to free up disk space). Contrast with Windows, where the problem is practically un-debuggable, or Linux, where once your problem goes off the rails of the config UI you'd better know how to use the command line.
- Comes with a lot of useful software (Pages, Garage Band, iPhoto, etc.), unlike Windows which comes with nothing (and a few toy apps like Notepad and Paint).
- You don't need to be a tech expert to buy a Mac. Just get the size you want and it works.
Contrast this with Windows, where every program looks completely different (makes Linux look consistent). Windows is user-hostile (forced reboots, resists creating a local account, I cannot edit the Send To menu anymore, etc.) The user-experience of Windows is the equivalent of the Big Ball of Mud design pattern.
Contrast with Linux, where you can do absolutely anything you want, but nothing ever fully works. If you had more time you could fix those little corners, but it's just not worth it. Or you'd have to add features to this app. Or your favorite window manager (Sawfish) gets harder and harder to install. Or you fight with Pulse Audio / Jack / ALSA for this particular sound program.
And if your primary value is spending as little money as possible, Apple will drive you nuts. For what you get, the price is fair, it's just that there's no option for a lower trim model. Don't need Thunderbolt? Too bad, you're getting a fast interconnect whether you want it or not.
The thing is, there is something intangible about high-end stuff that goes from "this does what I want and I don't think about it" to "I enjoy the experience of using this". It's a little like wearing high-end fabrics, or eating at a high-end restaurant. Necessary? Absolutely not. But it's that enjoyment it gives that creates the "fanaticism".