Apologies, but we don't push Dart. You don't have to use it. Google writes millions of lines of JavaScript a year and wants a better language, that's all.
As pcwalton says, SIMD.js evens an advantage that was in favor of Dart, while at the same time making JavaScript a better compile target for languages like Dart and asm.js languages like C++. It's also a really clean API that fits nicely onto typed arrays. What's not to like?