Legacy CUDA software would exist if OpenCL ecosystem was better. This is not the case. Code translation from CUDA to OpenCL is solution looking for a problem.
Ecosystem depends on CUDA, it doens't care where it's translated to, no? So it would work with translation, until it's properly rewritten to use open APIs. It's a solution for lock-in that limits your hardware choices, which is a problem. You don't need to look for the problem, it's pretty obvious.
And why not? If you can translate between them, it will help supporting legacy CUDA software. And new one can use new OpenCL to begin with.