However this decision does mean Apple can't produce monitors with more than about 200 PPI without the text being too small (at 200%). i.e. they can't go beyond 5K at 27".
Which is a shame, you can use 8K monitors with Windows at e.g. 300% just fine.
They can easily add support for rendering at 3x. iOS has supported that since iPhone 6 Plus. The only thing that's missing from macOS is a switch to turn it on, and produce all the UI assets at 3x.