Because under the hood x11 code is such a hacky mess the developers found it easier to start from scratch than add new features like HDR and VRR to x11.
If new features don't matter to you, there's still plenty of distros and DE's and WM's that ship x11 and will continue for a very long time.
So you're arguing that the historical context of Pooh"s design matters, and I fully agree.
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Would it make a difference to know that these are the original designs? Would you consider the original designs to be permittable?