Why should Google have to worry OEMs start to push out updates, they're responsible for the Nexus line and that's it. Google isn't building and distributing every Android device. How many low end Android phones are out there because OEMs can't stop pushing out devices? Google says here you go OEMs, do with it as you please. It's almost like raising a child (which I'm in the beginning stages of figuring out), you can tell them every move to make, but at some point they have to learn for themselves what's hurting them.
I'm wholeheartedly on the OEM/carrier blame train. Android is not iOS, and Google is not Apple. While there are similarities, they differ greatly on their approach. Apple has more control over their one phone, but that's all you get is one option. Google gives you choice, but that also means you can make the wrong choice. It also means OEMs have a choice to maintain their product borrowing the OS. If Apple and Google both went the same route, there wouldn't be such a huge rivalry, which ultimately pushes both sides to compete. And ultimately give us great devices.
Google does a great job keeping their products up to date, their products are the Nexus line. Google can't and shouldn't control what Samsung, Motorola or any other OEM puts over the top of Android outside a Nexus, that falls on the OEM or the carrier.
Sent from my Nexus 6P