Safe from monopoly control over Web standards.

The Web has been a consensus ecosystem, and Google does not have a track record of proposing reasonable standards. In my mind this is most grossly evident in the case of PNaCl, which was tied to their Pepper API and effectively impossible for non-Blink browsers to implement.

Google pushed for PNaCl to become a Web standard, and it was only through years of difficult effort that Mozilla was able to show AsmJS as a better solution, which eventually gave rise to the reasonable standard of WebAssembly.

Were Google in a monopoly market position back then, they would have pushed PNaCl, and non-Blink browsers would be unable to render the modern Web.

That might sound fine if you believe that Blink is the be-all-and-end-all of Web technology. But we have Servo now, and we already know better.