The lua ecosystem is extremely simple to embed in a native application, which, as someone who has had to do it, is something that feels underappreciated. Python and javascript were harder to set up for embedding on the same computer, and all but impossible to cross-compile for iOS. The simplicity of using lua as a scripting language in larger applications makes it a great target for compilation.

MoonScript also gets rid of a lot of the more verbose parts of lua, and replaces them with CoffeeScript-like versions. For example: shorter anonymous function syntax, syntactically significant whitespace, default local variables.