Dart is more than just a compile-to-JS (transpiler) language, if you have a look at Flutter, you'll see that it'll replace Java and Swift for mobile development as well as get rid of having to use Cordova / Phonegap; one language to build native apps on both mobile platforms and sub-second recompiles + refreshes.

You also get both Angular2 and React in Dart flavours, many developers who come from a Java or C# background just doesn't like JavaScript due to its inconsistencies, so obviously Dart gives a great middle-ground between Java / C# and JavaScript - it's optionally typed, so if you want strong typing, you can do strong typing, if you don't like strong typing, don't use it.

It can also be used as a backend just like NodeJS, although most of the focus is going into the transpiler and mobile part, the backend part is solid as well.

Less and Sass compilers as well as the build system you get out of the box, minification is built-in and unlike JavaScript, the language is very consistent, haven't had a WTF moment with it yet.

Dart also runs on ARM processors meaning you can build very lightweight applications for Raspberry Pi and similar devices.

I'm personally using it for business applications, have 3 systems in production with huge Dart codebases and busy with a tablet application now also using Dart.