Phone Mfg's will sometime release manufacturer-specific API's for Android that will only work on their phones.

I've always been disappointed at how/why Google allows fragmentation.

It certainly seems to me that they have the power to force a reunification in Android (and that if they did, the world would cheer).

Why not tell Samsung that Google must determine the update schedule, not Samsung? And if Samsung adds non-standard hardware, they must provide working updated code by this schedule.

And if Samsung doesn't like it, they are welcome to move everything over to their Tizen OS.

Even if Google cannot fix the past, why not do this going forward?

Google doesn't control Android after they release it. It's open software (which is why Samsung gets to "skin" it the way they do) and Samsung could add anything they want or even rip bits out. It's not Google's decision.

Edit: this is a lot of downvotes for no comments. What's wrong with my comment?

The downvotes might be because you're slightly mistaken about the level of control that Google possesses. While the code base of Android itself is open source, that means little because Google apps such as the Gmail, Maps and the all important Play Store are not part of AOSP code base. If a manufacturer wants to include those (and lets face it, they have to) they need to agree to several onerous terms and conditions that Google stipulates.

An example of such a condition is that if a manufacturer makes any phone that includes Google apps, they must not manufacture a phone that runs without it. This is why Amazon had such a hard time finding a manufacturer for their Fire tablet/phone. As for skinning, Samsung can only do that because Google explicitly allows it.

Lastly, I feel that someone should have pointed this out instead of downvoting you.