When you suggest its the most expensive, no doubt you are not including the fact it is a complete desktop, with all the cards you need, all the memory, and it includes the monitor.
...and if you
didn't want that specific size/resolution/format monitor, tough. If you wanted more than the default sized RAM, SSD, prepare to be reamed for 2x+ the market rate (or take a pizza cutter to your brand new Mac to DIY). If you need half a dozen terabytes of spinning rust for bulk storage (still the most effective way of storing large media files) bye-bye "all in one desktop".
Now when you get your high end PC, you get a box, with a CPU in it, and many upgrade to a different video card, different ethernet, additional PCI or other boards, all of which give the potential for some serious complications in configuring a working machine
Except (a) there are plenty of PC builders who will assemble, test and guarantee a PC with your choice from a huge range of alternative components, storage configurations etc. and (b) doesn't sound like you've assembled a PC since sometime in the early 1990s - a modern motherboard usually has a shedload of USB-A/C, Thunderbolt if you go looking (largely redundant on a PCIe machine), Ethernet, sound, NVME SSD slots, SATA connectors, often wireless built in. If you need "additional PCIe or other boards" it's probably something that simply isn't available - at least as an internal option - on Mac. I
will give Apple kudos for what they're doing promoting 10G Ethernet at reasonable prices - but still, most people don't have teh wiring, and if you do, adding it to a PC isn't that hard.
Of course, if your workflow revolves around Logic Pro, FCPx or some other Mac-only software (and have loads of legacy files that you need to access) then "switching" could be an expensive option in terms of time, re-training, new software etc. so that's a perfectly fine justification for choosing Mac. Unfortunately, for the last 10 years of so, Apple have pretty much been relying on that at the high end of the Mac range and not even attempting to compete with PC/Windows. Show an iMac Pro or Mac Pro to someone who
doesn't have some sort of pre-existing investment in MacOS, and they'll likely laugh in your face.
Apple Silicon is a chance for Apple to fix that by finally making something that
isn't just a PC clone in a designer box with a MacOS license.
Some "pro" users of Macs seem to be in the privileged position of
not having to justify every cent they spend on computer hardware... which is nice, but not universal - esp. for people who aren't their own boss and have to deal with a bean counter who's only agenda is to reduce the equipment budget and doesn't give a wet slap about the affect on any other department's bottom line.