From my point of view, it's a few things
1) They make genuinely nice bits of kit. whatever you think of the internals, repairability, OS etc. the hardware itself is generally thought of as attractive, good quality, great screens, the best trackpads in the business, nice use of aluminium for a lovely chassis that seems to last for ages. their stuff is slim, and for all that geeks complain, people like things that are slim and light. also people like using nice equipment, and apple stuff is nice. I tend to be in the camp of thinking that it's not that apple make expensive hardware, it's that they don't make cheap hardware, if you can appreciate the difference? though the prices on the 2016 MacBook Pro did make me blink a bit ;)
2) macOS is pretty good. although it's a fairly normal (though I feel attractive) take on a WIMP interface, it's unix (TM) underneath and you can pull up a terminal window and mess about with sed and awk if you like. OS updates tend to work well and have usually not resulted in an older machine running like a dog (not always, but usually). most applications are usually fairly self contained and are installed by dragging their icon onto your directory structure somewhere, and deleted by simply dragging it to the trash.
3) iOS hardware is damn good. Their CPU's are very fast and efficient, the handsets feel premium. They pioneered not letting carriers mess about with the OS and when a new OS comes out, you either get access to it immediately, or your device is obsolete. no waiting for your carrier or vendor to produce a firmware update for you.
4) iOS software looks nice, and generally is smooth and nice. I think that (and this applies to apple in many different areas), if you're happy to work as apple expects you to work, then things go pretty well. and lots of people are happy to work that way. If you prefer to do your own thing, and make products work around you, then apple is going to be frustrating.
5) iOS has a great security model. not claiming it's perfect, but it's pretty good. default strong crypto, an easy to use fingerprint sensor on all their current devices. permissions to phone data sources (locations, contacts, photo's mic, etc) is determined on a per-app basis during use (not at install) and you can say no, and you can change your mind. If your password is decent then it's very difficult to get data out of an iOS device.
6) macOS has a fairly decent security model. very few listening processes, standard users have no access to system directories, sudo for admin priv's, requiring registered developers ID's for software before allowing for install (in default config), etc. I'm not one to say that the Mac has no malware, but almost all Mac malware is what I'd call a trojan, rather than a virus. Mostly it has to trick the user into giving it root so it can be evil, rather than just infecting you without your say so. This may not last for ever, but at the moment that's generally true.
7) "it just works". okay, so that's not always the case. Apple devices have their foibles like windows does, but mac's work as expected often enough for it to become a cliche. They've got enough applications in enough sectors to please most people. Microsoft office support, Apple's own numbers, and pages are surprisingly good.
8) Apple are fairly open that they sell hardware, and that the software exists to sell hardware. This means that they're not trying to advertise to you, or monetise your every action. They seem to have a good stance on defending privacy and having the balls to tell government's to go away when they feel it's appropriate. They're doing what seems to be their best to design hardware that they can't break into, even against the wishes of some big interests.
9) as they sell the hardware and the software, everything tends to integrate well together. The Apple Store is a nice place to be, usually busy, but I don't think the staff don't earn commission so there's little pressure to buy.
10) like with many OS's, there's an ecosystem. You don't want to lose the investment, both in money, time and familiarity in the apps you've bought or got used to.
Ultimately, I think that by and large, windows is as capable as macOS is. It's a lot better than back in the day, however Apple stuff generally looks good, works well, and there is a general opinion that it's easy to use and look after, which most people want.
(FYI, I have several bits of apple kit, but also a win10 gaming pc)
