You can’t really read into that. They are unlikely to let their competitors know if they have a slight performance/$ edge by going with AWS tech.
Anthropic is not going to interrupt their competitors if their competitors don't want to use trainium. Neither would you, I, nor anyone else. The only potential is downside. There's no upside potential for them at all in doing so.
From Anthropic's perspective, if the rest of us can't figure out how to make trainium work? Good.
Amazon will fix the difficulty problem with time, but that's time Anthropic can use to press their advantages and entrench themselves in the market.