Requiring the users to install 20 or more dependencies (@babel/, @postcss/, webpack-*, etc.) and write dozens of lines of configuration every time just doesn't feel right (or maybe it is..).
And we know what the developers need, they need to bundle a web project in a way that's optimised for production, js and css compiled to run on N (configurable) most recent browsers (optionally). But that's not that trivial in webpack, if it was, perhaps we wouldn't have so many abstractions trying to improve upon status quo.
Perhaps that's just an inherently difficult problem. E.g. there are many many ways to handle CSS, people use variety of transpilations such as TypeScript or Flow, projects have different requirements.
Another data point is that Parcel this problem in a much more "everything works automatically" way and it's really resonating with people.