Most LLM sucked at Rust at the beginning because there's much less rust code available on the broad internet.

I suspect the providers started training specifically in it because it appeared proportionally much more in the actual LLM usage (obviously much less than more mainstream languages like Python or JavaScript, but I wouldn't be surprised if there was more LLM queries on Rust than on C, for demographic reasons).

Nowadays even small Qwens are decent at it in one-shot prompts, or at least much better than GPT-4 was.