Nvidia dominates training moreso than inference, and mostly because of their hardware efficiency and not entirely because of CUDA. To dominate Nvidia, you have to beat their TSMC investments, beat their design chops and match their software support. The shortlist consisting of companies that can do that reads "Apple" and nobody else, which is exactly the sort of captive market Nvidia wants to conquer.
OpenCL has been pretty handy for inference on older cards, but I'd argue it's relevance is waning. llama.cpp has Vulkan compute now which requires a smaller featureset for hardware to support. Many consumer devices skip OpenCL/CUDA altogether and delegate inference to an NPU library.