IIRC (this could be old news) AMD GPUs are preferred in the supercomputer segment because they offer better flops/unit energy. However without a cuda-like you're missing out on the AI part of supercompute, which is increasing proportion.
The margins on supercompute-related sales are very high. Simplifying, but you can basically take a consumer chip, unlock a few things, add more memory capacity, relicense, and your margin goes up by a huge factor.
They are preferred not because of inherent superiority of AMD GPUs. But simply because they have to price lower and have lower margins.
Nvidia could always just half their prices one day, and wipe out every non-state-funded competitor. But Nvidia prefers to collect their extreme margins and funnel it into even more R&D in AI.
It's more that the resource balance in AMD's compute line of GPUs (the CDNA ones) has been more focused on the double precision operations that most supercomputer code makes heavy use of.
The margins on supercompute-related sales are very high. Simplifying, but you can basically take a consumer chip, unlock a few things, add more memory capacity, relicense, and your margin goes up by a huge factor.