That's an interesting insight. I think the reason has less to do with the languages being good for language development than it is about other language features. JavaScript is the Internet's only frontend language. For many C/C++ programs, users may write plug-ins only in Lua. The common aspect is that the users are forced into choosing the language for external reasons. Many of them see flaws in JavaScript and/or Lua and would like to write in another language instead. That's how I see transpilers coming into existence for these languages.