While Chrome technically does not have the kind of root program that other OS or browser vendors run, they have the ability to revoke trust for specific roots, plus other things, like enforcing CT for specific CAs. Given that there's already a root program that's being run transparently, there's not that big of an incentive to run yet another root program, IMO. Plus, while I'm extremely happy that Mozilla is running their own root program for various reasons, using existing OS APIs for these things seems like the cleanest approach (if you can't trust your OS to make these decisions, you probably have bigger problems and shouldn't run that OS anyway).