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AMD Quietly Funded A Drop-In CUDA Implementation Built On ROCm: It's Now Open-Source
(www.phoronix.com)
This is a most excellent place for technology news and articles.
Along with what the other comment says, they could think that the project is in a good position to stand on its own now. It may have needed the funding to get to a good place where people will support it, but I'd bet it's there now.