They weren’t interested in creating an open solution. Both intel and AMD have been somewhat short sighted and looked to recreate their own cuda, and the mistrust of each other has prevented them from a solution for both of them.
At least for Intel, that is just not true. Intel's DPC++ is as open as it gets. It implements a Khronos standard (SYCL), most of the development is happening in public on GitHub, it's permissively licensed, it has a viable backend infrastructure (with implementations for both CUDA and HIP). There's also now a UXL foundation with the goal of creating an "open standard accelerator software ecosystem".
I decided that I have to start looking at Apple's AI docs
Apple will sell you a machine with 48GB of memory for thousands of dollars but plenty of people can't afford that, and even then the GPU is soldered so you can't just put four of them in one machine to get more performance and memory. The top end 40-core M4 GPUs only have performance comparable to a single A770, which is itself not even that fast of a discrete GPU.