Well 5K is a niche resolution the majority of people don't care about since it's ultimately not necessary. Yeah there's always "muh macOS retina scaling" but there's PPIs that are good for non-retina too and most go for that.
So because of that, monitor manufacturers don't make 27 inch 5K monitors since that resolution is pretty useless on anything that isn't a Mac, and the majority don't need that resolution and are fine with just 1080p, 1440p, or even 4K (which that in itself is also is also a niche due to the performance requirements of 4K.)