Web Reflection: What Is Wrong About 17259 Lines Of Code
I can answer and it is pretty simple and they have answered already by the way, you seem to just failed to read it: They have the resource and the will. Which means they can put 30 or 100 developers into something for months and even years and pay them to do something that might fail epically and still they would not mind! While the smaller companies and single developers cannot invest months into something that might fail or just be useless.
On the 'why' - it is just an experiment. The high expectations are to be the browsers that 'runs it native' and maybe they believe it will give chrome and chromeos some better user acceptance. Or maybe they really believe it is a step forward.
Anyway, just let them be. AFAIK very little number of companies are using the other attempts: GWT, Closure library, Go and so on. If we leave it alone it might become just one more project of them.