To control it. If they are successful at making AMD cards competitive in AI, and I agree that what's missing it's only the software, that would create immense value for AMD. Too much to not have control over how it evolves. If they are successful it will not just be Hotz, he will hire other devs and an entire community will form around it.

Sure they could just fork it and try to continue development themselves, but the community and momentum might very well not go with them.