On the other hand Cinema 4D that relies on mac users, cause its very popular on MacOS, I suspect because the UI is one of the best for 3d app which matters a lot to mac users, not only has Metal support but it was quick to jump on Metal 2 support too
So it comes down to what your “customers” want. Unreal for example released a small fraction of games on macos the big whale is iOS so they could not afford not to support Metal 2 either, although their support extends to other APIs (Direct3d, OpenGL, Vulkan etc)
I suspect this is one of the reasons why Autodesk killed Softimage which was may popular on Mac platform. In any cases the vast majority of the mac apps/games have ported to Metal 2 so Autodesk is the rare exception and not the rule.
How Apple can force people to move to Metal ? They cannot even stop you from making an OpenGL port on MacOS on top of Metal or just separate as it exists now. They did not stop Steam from making MoltenVK (Vulkan on top of Metal).
MacOS has a very comprehensive set of tools and libraries that helps developers make software like this, including drivers.
Problem is people think because Apple maintain these projects that somehow is impossible to have them other way. That’s not true, NVIDIA release themselves CUDA runtimes on MacOS. Many vendors release tons of libraries on MacOS. Harware manufacturers make their own drivers for MacOS (like my MOTU sound card). Apple is by no means responsible for the existence of OpenGL or anything else on Mac and cannot stop anyone from making a new OpenGL implementation.
Another example is Python, it comes included with MacOS with native support for ObjC libraries but non the less the Python foundation maintains its own mac version as well. If Python was to be abandoned by Apple tomorrow , it would not affect it’s future on mac at all.
So the question here is why none cares about maintaining OpenGL on MacOS and not whether Apple forces you to move to Metal. Afterall we already have Vulkan on MacOS and is a very recent technology. Maybe just maybe people dont care about OpenGL as much as some raging devs on forumes and blog posts will have us believe ?