Also part of the reason Babel exists is to take the place of a macro system. Instead of transpiling array spread into a function polyfill, macros would just output the pollyfill into the AST. What’s nice about this is that since it’s userland, people can test drive new features. Rust did that for async/await. And the pattern matching proposal in JS is based off a SweetJS macro.
(Obviously not all language features can be implemented as macros but you get my point, right)