That nobody else seems to be trying hard enough, despite being well-funded and respectable companies. And until somebody does, we're stuck with NVidia/Cuda or half-working stuff that's way more hassle to prototype or build a product from.
To answer the question why there is not much competition, I would like to point out that the required expertise is very rare. Not specifically the chip design expertise but the expertise spanning both chip hardware and low-level software for such chip-specific hardware, that is all necessary to create the compilers, the frameworks and libraries and which can also plug-in well with the existing AI/ML ecosystem such as PyTorch.