5K/6K/etc panels are exotic and expensive specifically *because* only macOS needs them. There is not enough demand and not enough manufacturers interested to get involve.A 32” display would need to use a 6K panel to maintain proper Retina resolution and scaling. Such panels are still somewhat exotic and expensive, and would make it difficult for Apple to keep the costs down
If Apple improved the fractional scaling ability of macOS, Apple would be able to offer more cost-effective display products - I think there are lots of users who are used to non-Retina behavior in other OS or won't notice the absence of Retina resolution.