In the end, Nvidia kind of got lucky with their bet on AI. While CUDA has been a thing for a while, it was limited to mostly academic and workstation workloads. It wasn't until LLMs and things like Stable Diffusion when it really became popular.
Unfortunately for non-NV users, most of these AI workloads when run locally assume CUDA is present and it's a considerable effort to make them work on non-NV GPUs. It's fairly okay for common workloads like running basic LLMs and SD models, but as soon as you get into more advanced/obscure stuff the harder it gets without CUDA.