You didn't get what I was saying in the prev comment, I was stressing about devices which are being sold out of the box with outdated Android versions, updating old phones is also another issue to be addressed but bigger issue is new phones with old android. Because if new phones continue to launch with outdated Android versions, the fragmentation problem will never stop.
OEM customizations are necessary, because thats the biggest power of open source software. If everyone starts using stocl android, it'll become boring. Take a Motorola in one hand, and take a xiaomi on the other hand, they're so different, but still gets everything done in almost the same way. But that doesn't mean turning android into a bloated, buggy and laggy piece of crap like Samsung's older TouchWiz versions. Also, customization does not mean progress should be slowed down. Setting up competition will make sure ther will be a balance between customization and progress. (like Samsung's improvements to TouchWiz after Motorola popularity).
Google doesn't sell Android to oems bro, they give it free. They only charge for the Google services and apps to be pre-installed and tested. Moreover, though 2 years support by oems may be too much, in fact many of them don't even give 1 year support because if they did, from the 30% devices still in lollipop, many of them would be running marshmallow atleast.