We're talking input controllers, wifi, bluetooth, nfc chips, gyroscopes, amps and half a dozen other parts that never attempted to have drivers mainlined in Linux kernel.
It's a chicken and egg problem - they won't make updated blobs until Android doesn't include newer kernel. Android won't use newer kernel because that would block 2/3 of the phones from being upgraded because of Broadcom bluetooth chips alone - Samsung might decide they are better off forking Android than waiting for Broadcom.
Edit: Sony has a bunch of phones that can run on 4.4 kernel: https://developer.sonymobile.com/open-devices/