I would say that it's more that Bash is good at something and JavaScript is good at other things and just because they are technically scripting languages doesn't mean that they are naturally a good fit in each other's domains. The README's comment tends to point towards an idea that all languages that can write scripts are equally interchangeable and of all choices JavaScript is the perfect choice. To people that are working on a variety of scripts in numerous languages who all have individual advantages and disadvantages, it comes off as nonsense.