Customizability is Emacs' selling point. A higher level of extensibility necessary means a higher learning curve. I'd call it a learning curve rather than "barrier": it's certainly not difficult to make Emacs look good. Most people don't care how Emacs behaves OOTB because they want to customize every aspect of it. You might say it should look or behave better by default, but I'd rather the base stay consistent and simple (it fits the use case better). There are plenty of starter kits/distros that look good OOTB for people who want a better default experience.