If you look at the older Macs, they make decent Linux computers because the hardware is decent and many people still use them in some capacity or another. There is also a project to make Linux run on the M series Macs.

There are some issues with VMs and WINE that make the actual hardware & OS more appealing. I’ve heard of issues like the VM won’t start or there’s instabilities in the VM itself that makes things more difficult. Wine and compatibility layers like it can and do have issues with obscure software or it can’t run the software properly or at all.

Mostly companies who have platform specific software that would cost to much to replace or take to long to replace. There’s still companies that run ancient versions of OSs like Pre Mac OS X and Windows 95 because there’s simply no newer OS that can run a specific software besides that OS.

There really is an xkcd for everything.