The only thing I can think of that would give Amazon reasons to dislike Mythos / Fable is that Anthropic really ruined their Bedrock story by imposing data retention requirements that cross a red line in regulatory compliance. It's just possible that Jassy would rather have nobody use Fable than doing it on the basis of, effectively, a direct data trust relationship with Anthropic.

It is hard to plug it together into this still being in Amazon's interest in the long run, but I could see a potential scenario where there was some bad blood with Dario on it if he previously committed to completely air gapped processing from a data point of view and now he went back on it.