AKA the idea that the firmware/os/drivers are all bundled together and hacked to work on a given device simply doesn't scale. Its employment for engineers because very security patch, every upstream refactor, requires all those closed source patches to be rebased on the latest version. This might work ok if the underlying technology (linux) didn't change their driver APIs at the drop of the hat, or the device manufactures didn't play throw darts at the soup of ARM interconnects, ram controllers, and devices, everytime they spun a new generation of phones/tablets/chromebooks.
Apple can get away with the monolithic model because they have a half dozen fairly similar devices to support. There are android manufactures which have released more devices in the last 6 months.
Yah, google is trying to fix that, but without a hard line in the sand with respect to pushing non-core OS/driver functionality into standardized runtime firmware APIs (think powermgmt) and locking down the driver API (userspace or otherwise) and assuring that it takes a long time for API's to be replaced/upgraded/deprecated. The hardware/upgrade story will continue to be a mess.