Windows I believe still uses RGB subpixel AA, because OLED monitor users still need to tweak ClearType settings to make text not look bad.
That is not true. Apple still sells Macs that don't come with a screen, namely Mac Mini, Mac Studio, and Mac Pro. People use these with non-HiDPI monitors they already own all the time.
You're right that there's nothing stopping someone from hooking up an HDMI-to-VGA adapter for their 22" Trinitron from 2001, but that doesn't mean boat anchors are a meaningful market segment. It's not a consideration for why they should retain a font rendering feature for a modern OS. You're just going to have to suffer with fuzzy fonts for your retrogaming hobby.
So what is the "configuration they sell" for the desktop Macs? The Studio Display that costs way too much for what it is, so to no one's surprise, they're not selling all that many of those? Or the Pro Display XDR for which the stand alone costs more than an entry-level Mac Mini? Sure no one will buy a $1600 monitor to use with their $600 Mac Mini. They'll get a much cheaper third-party 2K one.
My impressions based on limited anecdotal data I've is that most people with mac mini are using it as their secondary device (everyone has a Macbooks). Everyone is using 27" 4k monitors. 4k monitors are not that far from 2k monitors, and I think most people who are preferring to buy 2k are gamers that want higher refresh rate that their GPU can support at 2k. But gamers are not using Mac's anyway.
My 34” monitor is only 4K but is “retina” at the viewing distance in my home office according to this calculator: https://qasimk.io/screen-ppd/
You can separately purchase whatever monitor you wish. There are now plenty of 27" 5K monitors out there. Asus, LG (for now), Viewsonic, Kuycon, others I'm probably forgetting. They're expensive as far as monitors go, but not as expensive as the Studio Display.
If you want a 2k monitor you can buy one and hook it up, but Apple isn't interested in making it look good. It's a not new decision, either. They stopped selling Macbooks without Retina displays in 2016. They haven't supported 2k scaling since the M1 Mac Mini over 5 years ago: https://www.macworld.com/article/549493/how-to-m1-mac-1440p-...
Apple is not a budget vendor. They're a premium vendor. That's not just what other people call them. It's what they themselves profess to be. That's why you can get an Apple Thunderbolt cable for $70. To Apple, if you buy a Mac Mini, yes they're expecting you to hook it up to a 4k monitor. They expect you to be getting a Mac Mini because you want a Mac, not because you can't afford a Macbook.
The problem with 27" 4K monitors is that you can't have integer scaling on them. If you set the scaling factor to 1x, everything will be too small, if you set it to 2x, everything will be huge, and macOS can't properly do fractional scaling because what it actually does is render everything into a 2x framebuffer and downscale that for output.
And besides, only supporting HiDPI displays doesn't mean one can stop striving for pixel perfection. I hate SF Symbols icons because they're sizeless. They're an abhorrent blurry mess on my monitor but they're also not all that sharp on the MacBook screen. If you notice it once, it'll haunt you forever. Sorry. They do look fine-ish on iPhones though because those use OLED displays that lack the notion of a pixel grid anyway.
Why don’t they produce 5K/6K monitors that allow for 2x integer scaling? The $1,600 Studio Display is only $1,600 because it has no competition.
Because 5K panels are probably more expensive to produce than 4K ones, and because that would only benefit Mac users since Windows can do fractional scaling just fine. I'm not sure about that but it might also be that not all GPUs used in PCs can drive monitors larger than 4K.
It’s one of the chief complaints I have with one of my mostly otherwise good x86 laptops. The 1.5x scaling the display needs has been a pain point on multiple occasions.
Where it falls apart is at densities any lower, for example it struggles on those awful 1366x768 15.6” panels that it seemed like every other laptop was built with for a while. Similarly 24” 1080p and 32” 2560x1440 are pretty bad.
Or it could have been the DirectWrite thing. I just don't remember where I read it.
I always thought cleartype was ugly by the way.