Meanwhile, no OpenGL, no DirectX, no Vulkan. Indeed, they are “Pro” machines.
This does however not mean that you can't use the other API's, it just means that when you are using macOS, you'll have to bring the API's with you, and that is totally possible.
In most cases, you're not using those libraries directly and using an engine instead, and most popular engines have support for the bigger API's, including Mantle, Metal, DirectX, OpenGL, Vulkan etc. You simply select the build profile of choice (or make a build that has it all) and build it to taste.
On top of that, if I buy a “Pro” machine, I want everything available and as much choices as possible; and I want them on OS X, not on Windows.
As for Metal, it is just Apple leveraging iOS marketshare. Nothing more, nothing less. It is a nice API, but one that nobody asked for.
Finally, speaking of engines, most productivity software does not use them, so your point is moot.
The reality is that the software aspect of the Mac ecosystem is a mess since Jobs died; and also the hardware is a mess for the last couple of years. Even XCode and related tools are nowadays not top-notch compared to Linux-based ones and modern Visual Studio.