This is because Angular uses reflection, which requires that the dart2js compiler retain a lot of code and metadata unless it's told what it can safely discard.
AngularDart 0.10.0 has an option to remove the use of reflection for release builds which drastically reduces the compiled output size.
AngularDart 0.10.0 has an option to remove the use of reflection for release builds which drastically reduces the compiled output size.