You can actually sort of do what you are asking. It was common before official support for languages to use node, and simply call out to a binary compiled for A

You can actually sort of do what you are asking. It was common before official support for languages to use node, and simply call out to a binary compiled for Amazon Linux. That does work. However, the support means that the Lambda system can call the specific binary directly, and that libraries are available to expose the data structures easily. There is nothing preventing you from calling a rust program from the node runtime for instance, if you wanted to.