If Chrome team actually cared about Dart and went ahead with Dartium's integration, Dart's future would have been much different.
Then the Angular team decided to dump Dart and go with Typescript.
So politics as usual.
And in addition to not having full support from Google, there was not and probably would never have been buy-in from Mozilla or Microsoft. Also the language IMHO didn't offer much more than JavaScript, and 6to5 -> Babel was gaining traction at the same time. It wasn't a good recipe for success.
I think it was smart of Google of giving it a fair trial and cut its loss when it was time before it got embarrassing or "coffeescript costly" for many developers.
The problem is that all of those new "beautiful" languages is that they trade pragmatism for purity, but at the end, we all have stuff to build, and at the end of the day, a well known, well tested, and good enough language with some modern construct (a la TypeScript and ES2016+) can become a very powerful tool to build small to big code base, whereas a beautiful near perfect languages would have brought us lot of development frictions or little exhilaration.
There is a reason why the Chrome team was not really into it, and they might have been right, but regardless, they should not be blamed for Dart's fall. As developers, I do not think we want another GWT or Google Gear kind of experience.
TypeScript is successful because it solves the right problem the right way, i.e., adding type without changing everything else around it.