First, you don’t have to pay the absurd prices. The Mac Pro isn’t the entire lineup, people tend to hang onto Macs a long time (it took a lightning strike to make me replace my 2008 iMac), and there are usually used/refurbished machines available for much less if you’re willing to shop around a bit.
Also, it’s 2019: why would price-sensitive buyers purchase any desktop OS? Android, iOS, and Chrome exist now. I get that some people need more power, but those people are generally able to make more educated purchasing choices, so seemingly obscure options (such as buying a late-model laptop with a broken screen and running it with a cheap external monitor) are much more open to them if price is a genuine concern.
Second, iOS. If you’re using iOS devices, they cooperate with MacOS much better than with any version of Windows. The next versions iPadOS and MacOS allow you to use an iPad as an external monitor. Then there’s iOS development, and even if you aren’t a real developer, it’s not too hard to use a Mac to compile and sign some common indie app types (like Java and Ren’Py) into iOS apps. Or if you never touch the power user stuff, then there is still the seamless exchange of documents between the iOS and MacOS versions of apps.
Third, MacOS is really good at working with other OSes. Most file types will just work, most Windows software will run in a WINE wrapper (which takes like a minute to setup with a free app like Wineskin), there are a couple of virtual machine options, and you can just dual boot into Windows if needed.
MacOS is actually a much more interesting hobbyist OS in a lot of ways. The UNIX is right there, if that’s your thing, and you can do a lot of tweaking, tuning, or compiling apps on your own.
The big deal is just the user experience. It’s subjective, and hard to quantify, but most people who use Macs also have experience with Windows, and the MacOS is still less clunky and more sensible. I can use Windows, but every time I boot into that partition I kinda regret it. I think it’s been like two years since I touched Windows on my home machines, so it’s a bit hard to remember which hiccups in my workflow annoyed me most. I haven’t found a game I needed Windows to run in a while now (mostly I use Wineskin to turn them into Mac apps), so I basically haven’t had a reason to use Windows. It’s subjective, and usually a matter of things taking one extra click in Windows (or the same things inexplicably behaving differently across apps), so it’s hard to use as a debate point, but working in MacOS is just more pleasant.
Seriously though, it’s 2019 — if you’re price sensitive you get more bang for the buck out of iOS, Android, or Chrome. Desktop OSes are for hobbyists and power users now, and either of those groups can figure out a way to use an OS they like at a price here willing to pay.