I attribute it to demand, due to differences in text rendering on Windows vs. macOS.Yeah, there are a handful of doublewide 2.5k (or whatever you want to call those) do have 240Hz support, I believe using DisplayPort 2.x. At least Samsung does not seem to support via HDMI.
This screen uses Thunderbolt 4, which is USB4 PHY. That requires DisplayPort 2.1. Interactions between USB4, Thunderbolt 4 and DP 2.1 are outside my realm of expertise. It may be however that they only have 2.0 controllers and not 2.1 controllers.
The 49" screens being driven at 240 Hz and this panel are possibly different technologies, and this panel may simply not be capable of being driven that high. Easiest way to tell there would be to look for a smaller sibling like a 24" 4k and see if it supports a higher refresh.
It is also worth noting that unlike HDMI which is a pretty bizarre cabling specification, DP is designed by VESA to be able to carry the signal all the way onto the panel, e.g. it is meant to be conducive to have all the internals be DP as well. So it may just be a matter of demand - Samsung is possibly recycling the panel tech that they built for Apple (who would be dual-sourcing with LG). Putting an entirely new 6 month old controller on the panel may just not be something they were going to do for what will probably be a lower-volume product.
4K 27" looks very good on Windows. 4K 27" on macOS is pretty good, but not as good as on Windows. Apple eliminated sub pixel rendering many years ago, and the quality of text on non-Retina and near-Retina screens has suffered.
On my 163 ppi 3840x2560 Huawei screen, text quality is quite reasonable even with a non-2X scaled resolution, but it's still just not as crisp as my 218 ppi 27" 5K iMac. This is at my ~22" seating distance, even though 163 ppi is mathematically supposed to be considered "Retina" by some at >21" distance, for 20/20 vision. I think something like 4K 24" 184+ ppi (Retina at ~19") would satisfy even more people, and 5K 29.4" 200 ppi (Retina at ~17") would be amazing. 5K 27" 218 ppi (Retina at ~16") seems like overkill for a fixed desktop for most, catering to the top end, but I guess that's how Apple differentiates itself and justifies the pricing for the Apple Studio Display.
The claim is not that the S9's matte finish is as good as Apple's nano-texture. The point is many people prefer it over glossy.I'd be a little skeptical about how that "standard matte finish" of the S9 compares to Apple's nano-texture. I have the nano-texture on a 2020 iMac and an Apple Studio Display, and it looks nothing like the "standard matte finish" on a cheap display.