Earlier quoted context omitted.
There are many reasons. First, Google didn't design anything. They were looking for partners for their OS and these partners used their existing design. The first HTCs were almost identical between their Android and Windows Mobile versions. Second, there are reasons why the embedded systems do not have them. Apart from increased complexity (bad for the designer and manufacturer), increased energy consumption (bad for…
Google didn't design the operating system? Microsoft didn't design computers either but they have been steering PC manufacturers for over 20 years since Windows 95 and the plug and play initiatives.
Microsoft basically strongarmed the PC vendors - they either did what Microsoft said, or didn't ship Windows with their wares. Windows, which was the only game in the town, if you wanted to sell PCs.
Google didn't have such luxury when they started with Android. They needed to be everyone possible to be with them onboard and the "lets throw out everything you have and design new hardware from scratch" doesn't make for a good start.
In mobile, Microsoft also reused Qualcomm's reference design. But contrary to Google, they used ONLY Qualcomm's design, that's why their system looks united. All the WP phones are basically the same board.