Recently Google has shown little interest in working with others; witness Dart (which essentially nobody but Google wants) and NaCl (which no other browser manufacturer wants).
Second, the position of every other browser manufacturer is that NaCl is undesirable because (a) it's not compatible with JavaScript, so it requires another language runtime and (b) that it locks the Web into x86 and ARM. As bzbarsky of Mozilla posted here [1], if Google had made and pushed NaCl a decade ago, the iPhone would be unable to browse the web. Google ignored the other browser manufacturers' concerns and are now pushing NaCl to gain a competitive advantage.
Sometimes the user doesn't know they want something until they see it in front of them.