A key reason to own a Mac would be to build iOS apps and MacOS software.
For me, the reason to own a Mac (besides hardware support and generally liking macOS) is the amount and quality of third-party software. There is a lot of software that I either need or want, and there are no good-enough competitors on Linux, e.g.: Microsoft Office (for work), 1Password, Affinity Designer, Pixelmator, Acorn, LaunchBar, Little Snitch, Tweetbot, Mic Snitch, DeckSet, Paprika (for recipes), Things, PDF Expert, Arq, Dash, Sonos, etc. In addition, a lot of these tools and macOS are very well integrated, e.g. I can directly search Dash or 1Password from Launchbar. I can make a phone call to a person directly from Launchbar, etc.
For some work there are better open source tools, e.g. Emacs as an editor, org-mode for notes/outlining, LaTeX for typesetting, Handbrake for video transcoding. But they all work fine on macOS.
Oh, that same old argument. No they're not. Absolutely not even close. This is coming from someone who actually uses linux 90% of the time every day. Linux on the desktop is still a huge mess, every desktop environment on linux is a real pain to use, I won't go into details, but those who use linux daily on the desktop cringe reading comments like this, unless using a wm like dwm or i3, but those suck BIG TIME too if you ever have to leave the terminal.
Or you know, to have a UNIX, but also a nice just-works-most-of-the-time desktop UI, device support (for stuff like external audio interfaces, scanners, etc) and access to all kinds of proprietary pro apps, from Above and Microsoft to whatever.
A key reason to own a Mac would be to build iOS apps and MacOS software.