They didn't see the point/understood how this could be important, at the time.
Cameras are shooting 12-25 bits of dynamic range. Displays can't yet render this, but the data is being captured and better reflects what the eye can see as it adjusts looking around a scene. This gives a lot of latitude when processing RAWs (sensor data) to render out a final image in a chosen format (Currently commonly SRGB 8bpc but moving to 10bpc 709/2020)
No reason paintings or created works couldn't also fill out at least a ~24 bit dynamic range similar to audio (Hence the move to 10bpc, which gives roughly ~1.07e9 (2^10)^3 possible colours compared to ~1.67e6 (2^8)^3)
In painting this would let you have a lot more contrast before blowing out a highlight (hitting the digital limit in brightness representation and clipping or losing information), and a proper tonemapping curve combined with dithering can fold this down for lower capability displays. This also gives you a lot more range to work with when digitally colour mixing.
A similar thing already happens with 3D rendering workflows in Blender/C4D/Maya/etc. where an output curve is applied for tonemapping and colour correction.
This lets you work in an unconstrained space for processing/creating and then incorporates a mastering/release specific step for rendering out to a given display format. The great part is, as technology improves the original work can just be displayed as is. (Think about the progression from wire recording -> tape -> cassette -> CD -> direct master renders sold in lossless file format)
There aren't yet that many people using HDR screens. Even 4K is still kind of a niche in most parts of the world as most people don't replace their TV more than once every 10-15 years and when it breaks they aren't necessarily ready to pay a premium for a quality they haven't experienced yet.
It is always the same issue. Why buying better stuff if there is no content and why make content if there are so few users? [1]
[1] the answer is porn.
