Choice of tech stack is not merely a question of performance, but also portability and packaging. Self-contained, compiled static binaries are much, much more portable than shipping full script runtimes (JS/Python), dealing with the inevitable spread of runtime versions installed on everyone's machines, and dealing with the version spread of the dependencies installed separately.
> All the CLI does is take command line arguments, put together requests based on them, send them to an API, get the responses, do mild transformation on the responses,and output it to stdout/stderr.
This is an argument in favor of a language like Go, arguing that the garbage collector in the runtime is inconsequential, over a language like Rust. It is not an argument for shipping a script runtime.