My only guess is they have a parallel skunkworks working on the same thing, but in a way that they can keep it closed-source - that this was a hedge they think they no longer need, and they are missing the forest for the trees on the benefits of cross-pollination and open source ethos to their business.
Do you expect them to be able to capitalize on the AI fad so much (and quickly enough!) that it's worth dropping the ball on projects they're now doing well in? Or perhaps continue investing into the part of the market where they're doing much better than nVidia?
So, again, it's not at all clear that AMD being in the compute GPU game is the automatic win for them in the future. There's plenty of companies that killed themselves trying to run after big profitable new fad markets (see: Nokia and Windows Phone, and many other cases).
So let's examine that - does AMD actually have a good shot of taking a significant chunk of market that will offset them not investing in some other market?