I've also heard some handwavey explanation about how certain parts of the panel manufacturing process is essentially separated by DPI. That you can reuse certain aspects of a ≈ 100 DPI manufacturing line across varying refresh rates (and physical sizes).

Then those line can probably serve a large part of the gaming / normie market, while the ≈ 220 DPI (e.g 5K @ 27") have a very small market.