[ehnto]

It's because browsers are the target deployment environment, and browsers move pretty slowly (although a lot faster in recent years). So to use modern language features (such as ES6 or Typescript) you have to transpile back to older JS. For many projects, I don't personally think it's worth the tradeoff of tooling setup and dependencies, so I won't use it in those cases. But for decently complex projects it is nice to use modern language features.