...unless Google wants to become an hardware first company and believe Mot can outdo Samsung and Apple in hw design (given their track record, an extremely naive assumption) of course. such an announcement would kill Android leverage in no time leaving them with nothing.
Android dominance is currently based on a soft power, where competitive interests of HW companies, software houses and carriers are playing out on more or less level playing field, and it's based on a very volatile balance. One that can be crushed with one bad move such as this one.

The Motorola/Google handset route is dangerous because if it results in a handset that actually sells in quantity it is the other Android OEMs, including Samsung, who will suffer.

Google must be unhappy or at least disconcerted with how the Android OEM ecosystem has turned out. One must presume that by releasing Android Google had hoped that there would develop a healthy and diverse OEM community which would allow them to sit above, it a bit like Microsoft had done with Windows OEMs, except this time Google would make it's money from the bundled services rather than software lisences.