Likely because of their "20% personal project time" policy. As best I recall, ChromeOS started as a personal project to see if one could build a OS around a we

Likely because of their "20% personal project time" policy. As best I recall, ChromeOS started as a personal project to see if one could build a OS around a web browser (and Google already had one handy). On top of this Android didn't start within Google. And Rubin ran it as his own fief. Supposedly he insisted that all Android devices come equipped with a mobile radio, and thus Google would not certify WiFi only tablet devices.