Dart is indeed a cool language but there was a huge resentment when the Dart VM was about to be shipped with Chrome and create a Google only web. It's a great burden for the language, I hope it could succeed without being put under our throats.
Not some support for other languages on a first class basis on the webpage just like Javascript (which direct access to the DOM and everything).
Besides, I'd much rather have the effort go into one new VM (or VM "mode"), so we can solve the problem once and for all. That is, let's have Web Assembly.