https://www.anthropic.com/engineering/advanced-tool-use
They discussed how running generated code is better for context management in many cases. The AI can generate code to retrieve, process, and filter the data it needs rather than doing it in-context, thus reducing context needs. Furthermore, if you can run the code right next to the server where the data is, it's all that much faster.
I see Bun like a Skynet: if it can run anywhere, the AI can run anywhere.
Also, Java's ecosystem is unparalleled (top 3 in size, depending on domain it usually has the best packages (e.g. typical backend-related functionality)), has stellar performance, a huge developer base, best-in-class IDE support, even LLMs understand it exceptionally well (given how widely represented it is in the training corpus, plus has a decent type system) if that's your thing.
For a typical backend system, you really have to have a good reason to choose something else at this point.