The messy truth is that Google has created only a half-open ecosystem. 98%+ of Android users are at the mercy of the carriers and handset makers for updates. That's not a truly open ecosystem.
Even if 100% of users were at the mercy of carriers and handset makers, that just underscores that 'Google can't "do something about it"'; it doesn't even mean the platform is not "open", as you are mistaking open devices for open software: the platform is, in fact, so open that carriers and handset manufacturers are allowed to make arbitrary modifications and sell closed devices running the result.
Shorter saurik: "Android is so open it's closed!"
Google has created an open ecosystem, and these are the natural consequences. Google can't "do something about it" because of the open terms of their licensing.