I don't think anyone expects the Android OS to be a collection of entirely open source device drivers.
Those proprietary drivers are specific to the myriad of hardware that the OEMs are running the OS on. You can still run Android on any hardware you have the drivers for, or emulate it in a virtual machine.
Those proprietary drivers are specific to the myriad of hardware that the OEMs are running the OS on. You can still run Android on any hardware you have the drivers for, or emulate it in a virtual machine.