Does your OEM create their version of Windows? No, they ship the binaries they receive from Microsoft. As long as Android OEM's are allowed to build their own version of Android this problem will always be in the hands of the OEM.
There's a pretty huge difference between modifying the os and its desktop environment compared to just adding a few extra bloated apps and some wallpapers...
There's a big difference between an OEM merging their source code with Google's AOSP source code and then compiling it to build an OS than just adding crapware to a Windows installation. OEM's can't modify the Windows source code and can only distribute the OS given to them.
