Lisps are hackers' languages - programming languages made for writing programming languages. The following applies to Common Lisp at least, if not others. It

Lisps are hackers' languages - programming languages made for writing programming languages. The following applies to Common Lisp at least, if not others. It is homoiconic and most implementations are written in Lisp. It is very open, in that you can inspect existing structures from the REPL. It has a long history and was the language where many common software paradigms were developed. It comes with powerful builtin tools like a debugger with restarts where you can make changes to the system live. The core language is very small but doesn't constrain what can be done with it.