One could. But let's suppose Google provides the contributors making up the bulk of the people with key responsibilities on the project for five years and then

One could. But let's suppose Google provides the contributors making up the bulk of the people with key responsibilities on the project for five years and then decides to withdraw them. It's possible for the project to continue and be healthy, but you are going to face a large disruption. You're suddenly going to need to fill a lot of key positions -- developers, designers, managers, etc. The direction of the project could change radically as the new people controlling the project don't share the same vision for it as the old ones. All-in-all, it is likely to prove fatal or cause a radical transformation, and the resources for enhancements are likely to be much more modest.