why?
Because bash feels clunky to write and work with for anything non-trivial, especially compared to other scripting languages.
Why not another scripting language (no compile necessary)?
Because bash and sh are installed nearly everywhere. Any other scripting language means the user is required to have that installed, and that is far less likely to be the case.
If I could write my scripts in a nice syntax, but be sure my users will be able to use it effortlessly by distributing to them compiled versions, then that would make both of our lives easier!
Thoughts? Are there any languges that do this?
Almost, but you bring up an important point about other language support.
The code includes an install script for one language, and the second part about "any language" isn't quite right. There is an alternative way to get any-language support but the current approach requires a language to have a syntax that is compatible with bash/powershell. For example I abuse the hell out of multi-line strings and multi line comments in javascript to make it be interpreted as a do-nothing bash/powershell script.
Python specifically might be possible because of its triple-quote strings, I haven't spent a long time trying but I did try a bit. However in general I don't think languages, like Haskell or Elixr, can work in this form because their syntax is incompatible.
However, if you don't care about being able to edit the script, it should be possible to mangle code from other languages, like converting Haskell code to hex or some other escaped format (can't be binary because that's not valid bash/powershell). We'd need to handle unpacking that hex with shell/powershell, but it could be done. And in that case, yes it would work with any portable language. (And many are more portable than Deno, which struggles to run on old stuff like Ubuntu 16.04!)
If you're interested in the hex unpacking let me know. I'm working on an offline bootstrapping script for deno, which involves embedding the runtime binaries of all OS's as hex into the script itself. Once I make it, it should be a lot easier to get this kind of thing working for other portable runtimes.