Maybe because Apple got pissed on how Khronos took over OpenCL, AMD and Intel never offered tooling on par with CUDA in terms of IDE integration, graphical debuggers and library ecosystem.
Khronos also never saw the need to support a polyglot ecosystem with C++, Fortran and anything else that the industry could feel like using on a GPU.
When Khronos finally remember to at least add C++ support and SPIR, again Intel and AMD failed to deliver, and OpenCL 3.0 is basically OpenCL 1.0 rebranded.
Followed by SYCL efforts, which only Intel seems to care, with their own extensions on top via DPC++, nowadays openAPI. And only after acquiring Codeplay, which was actually the first company to deliver on SYCL tooling.
However contrary to AMD, at least Intel does get that unless everyone gets to play with their software stack, no one will bother to actually learn it.