If you ever get the chance to write something in OpenCL and then in CUDA I promise you will understand immediately why Google didn't push for it.

There is a lot more boilerplate to it, read/write to the buffer, queueing being handled explicitly. Here's an example that illustrate what I mean: https://github.com/rsnemmen/OpenCL-examples/blob/master/mand...

For comparison here is an implementation in CUDA: http://selkie.macalester.edu/csinparallel/modules/CUDAArchit...

Notice how the CUDA code is more readable.