The flash memory on the Nexus tablet was pretty poor quality. Like many Android devices of the era, eventually you get higher and higher rates of read failures

The flash memory on the Nexus tablet was pretty poor quality. Like many Android devices of the era, eventually you get higher and higher rates of read failures which makes the error correction try again and again to get a good read massively reducing disk performance. It's hardware falling apart. I've had several Android devices from several manufacturers experience the same issues whether or not they got updates.