GPU compatibility

It's not Adobe leaving Mac users behind. Apple totally blew it on 3D decades ago through lack of interest, a somewhat snooty attitude toward video games, and lack of support for developers.

Back in the day, CGI, CAD, and game developers went where they found collaborative industry partners, and Microsoft was a big supporter. The result is that Windows and, to a lesser extent, Linux have been where the action is on 3D for decades. (It's not just games. Most 3D-related features in AutoCAD are Windows-only. Maya is cross-platform but Windows has far more 3rd Party plug-in support and performance is significantly better. Solidworks is Windows-only; so is 3ds-Max.)

Most gamers are on Windows or consoles, so if you're creating a tool for character design, the expense of developing for the Mac wouldn't be all that easy to justify. Mac was anti-Nvidia for some reason, giving startups another reason to ignore MacOS. Nvidia has been at the cutting edge of 3D rendering for a long time. They're just better at it than anyone else, especially with ray tracing now in silicon. Basically, everything in 3D runs faster on Nvidia hardware and it is much easier to code. Modeller, not coincidentally, was developed using the Nvidia API. It was created by a startup that Adobe acquired. As far as I know, only Dimension and Stager were developed in-house.

Windows is fine. Today, it's at least as feature-rich and the differences aren't that hard to learn. In the Adobesphere, the OS-specific bugs are pretty evenly distributed, so you're not losing out there.