Looked at the code for literally every framework out there on TodoMVC (including clojure, clojure+om, and dart+angular which are not on there). Everything else just looked too bloated or overly complex. Dart had a decent amount of code but it also had the great readability.
Warning: AngularDart 1.0.0 was just released so the documentation is lacking (it references 0.1.0, an order of magnatude of an earlier version)
Why not Java?
Because we use it everyday and crave something new.
Why not Javascript/Coffeescript/IcedCoffeeScript/TypeScript/LiveScript/...?
Couldn't decide on the dialect.
Couldn't decide on the build tool (Yeoman? Brunch? Gulp? HALP!)
Dynamic typing
Why not Scala?
Good question.
Why not Clojure/script?
Not everyone is on board on the LISP type funktional languages
Went with Go and Dart for a few reasons.