I'd argue that while Apple
serves those markets, it hasn't
catered to them for a long time, and it would be fair to say that in many cases it's downright neglected them.
There's a whole lot of people who are in the 'pro user' market who are incredibly frustrated with Apple - slow on hardware refreshes, generally way behind on chip generations, and a focus on design over reliability or performance.
The thing that stops a lot of people from migrating away is a lack of better options.
Some are tied to the Apple Ecosystem, and so there's no legit way of running OSX on non-Apple hardware.
Others don't need to use Apple, but Microsoft in the Windows 10 era is arguably worse, and they still haven't figured out that they need to fire all those people who keep pushing user-unfriendly choices like changing defaults on already installed systems, pushing app store apps down people's throats, etc.
For those who could move to Linux - there's a lack of nicely designed hardware that has all the modern bells & whistles, and that doesn't have weird software quirks. Particularly in the mobile space, but also to an extent in the desktop space, too.
Even when you look at a PC builder like System76's systems, their laptops still look like something out of a catalogue from 10 years ago, with none of the clean aesthetic and polish of Apple, or even premium Windows laptops. The desktops are better on that front.
Sure, you could, like I have, run a modern Linux distro on say a Lenovo X1 Carbon, or a HP Spectre X360 if you want something that looks pretty decent and has good performance, but even they have weird hardware quirks. Sound, for instance, is amazingly frustrating, and something I have to mess around with regularly, sometimes multiple times a day. It makes me look like an incompetent idiot when I'm talking away on a conference call to discover that for some bizzare reason, between Firefox/Chrome/Chromium and the System sound settings - what was working just fine not 30 minutes ago has decided that it no longer wants to cooperate, and has switched, yet again to a profile I don't want and don't need.
On the desktop side is no better - the few companies selling desktops, are mostly selling overpriced garbage aimed at Windows users, so you need to go through a Custom PC Builder using enthusiast equipment, which means spending half your time trying to find out if the 50W of RGB LEDs that the damn device comes with can be switched off (Answer: Probably not, unless you run Windows, or are willing to pull out a soldering iron. Which makes for a great discussion if you need warranty support on something).