Could the reason for AAX version from Red Rock Sound not working in Pro Tools be the following taken from the bottom of their landing page? Note the last section starting with "In theory":

Spoiler: System requirements

All Red Rock Sound products require a computer with appropriate DAW host software (none of which are included).

Plug-in Activation requires Internet connection!
You can go offline as soon as plug-in is successfully activated.

Versions from 1.0.0 and newer of the Red Rock Sound plug-ins have the following minimum requirements:
Mac OS X 10.14.6 or higher for AU.
Mac OS X 10.14.6 or higher for VST.
Mac OS X 10.14.6 or higher for AAX. Latest version of iLok license manager.
Windows 7 or higher (Windows XP not tested).

Mac: Intel Core i3 / i5 / i7 / Xeon / Full Apple silicon support (M1 or higher).
Windows: Intel Core i3 / i5 / i7 / Xeon / AMD Quad-Core or newer.

In theory, any AAX, VST, VST3, AUv3 compatible host application should work. However, due to plug-in host differences between DAWs - and our own rigorous testing standards - we only officially test our plug-ins and instruments in the most recent versions of Pro Tools, Logic Pro, Cubase, Ableton Live, Studio One, Reaper, and Bitwig. Red Rock Sound plugins are not tested in non-listed systems, but they most likely work as long as the system requirements are met. We cannot guarantee a solution for issues in unsupported systems.

Could it also or instead be that the newer teams just have not figured out or put in the time to figure this out?

I personally appreciate the teams & suppliers that allow us to test product before laying out funds and then regretting it. Just a curious thought.

 

Are there no demo versions available to test? The famous Red Rocks concert venue is located in Colorado. This developer is not, so that would present an issue of its own about buying them at this point in time. (for me).

"Mac OS X 10.14.6 or higher for AAX. Latest version of iLok license manager. "

This presents another possible issue, for Mac users. I am not sure why this is not mentioned about the other plugin formats for Mac. But I would guess that they will not load as modified AU plugins inside Bluecat's Patchwork if iLok is required for the AAX native versions.

Maybe these issues can narrow your thread scope to the Windows versions. iLok being involved in the details means this probably will not happen for any Mac plugin host anytime soon.