But bash is installed by default if I'm not terribly mistaken, and it's classified as an essential package. If you put in a bash shebang, it should work.
There's like five comments from you in this thread and you seem very adamant about people not writing bash scripts. Have you considered that not everyone has the same requirements? Maybe they don't care about targeting systems that don't have bash installed. In that case, they can use the myriad of enhancements that bash offers to improve their productivity and happiness.