Should a bundler really include all those features though? All I want out of a bundler is to bundle. As soon as it starts doing transforms, we end up with applications that only work with that bundler.
If you're building a modern web app, you're likely using more than just JS files. The compilation target is complex, and there's room for more optimizations when the bundler is aware of the app as a whole.
Parcel is here because most people don’t need to just bundle but also a whole pipeline for optimization and extended browser support (Babel)