It's more of an issue on the end user's side. All the main browsers have had support for ES6 and newer features for years. But that doesn't mean end users are running the latest versions of those browsers. So when you transpile/polyfill a feature, you're aiming to support that small number of users who haven't updated their browser in 5+ years. If you don't care about those people, you have no need for that intermediate step. Or if you want to be really sophisticated, you can look at the user agent for an incoming request and serve a response that's transpiled/polyfilled exactly as much as is needed.