And is it really worth it? As someone all in w/ Dart (I chose to build my product with it), dart2js serves me well, and the resulting JS is said to be more performant than raw JS. JS itself is improving (see ECMAScript 6 and TypeScript), which means Chrome's compiled JS will improve with it. Of course, having the Dart VM in a version of Chromium they call Dartium has been important, as it eliminates the need to compile until I care to test on other browsers. But there's exciting work ongoing on incremental compilation, so that in theory you'd just see your results in any old browser (http://goo.gl/EHJcK9) a la interactive programming. Bottom line: the Dart development cycle is already great and always getting better, no VM in Chrome needed.
As well, the Dart team can focus on more important priorities: the incremental compilation I mentioned, better JS interop (it's not bad now), improvements like async/await (coming in 1.9), even better concurrency primitives (see Fletch), Dart for native apps (again see Fletch) and more.
And remember, this decision can change later when the climate changes or other factors are in play. But for now, it makes a whole lot of sense to abandon any push, or notion thereof, to get the Dart VM into Chrome.
IMHO, Dart (I mean the language, libraries and tools combined) is hugely underappreciated. Folks will continue to focus on improving it and building awesome apps with it, and this news should quiet some of the noise.