Hardly surprising because I don't think there's even one piece of high-end CAx software for Mac.
For CAx in general it's difficult to say, because there's such a huge variety of software and every little niche has its own highly specialized (and usually very expensive) tools. I've never seen any of these support anything other than Windows and/or Linux. Some of them have Win32 GUIs and Linux is headless only (for running simulations), some are fully cross platform, some are Linux-only.
Most CAE engineers around here work on Linux, mainly because they prefer how easy it is to script and automate things and because the headless HPC/batch environment is of course also Linux. Meanwhile CAD and design only happens on Windows because CATIA is Windows only, like the various Autodesk tools used for CAID. From the late 80s to the early 2000s this place had a ton of UNIX workstations (SGI, HP, Sun) and even UNIX clusters (IRIX and SUPER-UX among others, the latter having virtually no representation on the internet today). There's also still IBM AIX systems around, as well as IBM mainframes. Not my department though.
Suppose something like CATIA was available on Mac and offered lets say a performance benefit. Would you consider Mac? Or would you for example still need a whole other set of tools to be available as well for it to be even possible?
Are you saying some people still use IBM mainframes for CAD/CAE/etc applications? If yes, that's unexpected yet intriguing information, and I'd love to know more.
Although maybe you were just stating the obvious that IBM mainframes survive in general even if no longer in this particular domain.