One of the security enhancements that were announced in Android 5.0 Lollipop was that data encryption can be enabled by default on all new devices but eventually it will not.
Google backtracked with this new security feature, merely encourage manufacturers to enable encryption of data without forcing as we can see in the document of the Program Compatibility Android 5.0 which details the requirements that must be met by manufacturers to launch their devices with Android.
9.9 Full-Disk Encryption
Implementation If the device has a lock screen, the device MUST support full-disk encryption private data of the application (/ datapartition) as well as the SD card partition if it is a permanent, non-removable part of the device. For devices supporting full-disk encryption, the full-disk encryption SHOULD be enabled all the time after the user has completed the out-of-box experience. While esta Stated as SHOULD requirement is for esta version of the Android platform, it is very strongly recommended as we expect change to esto a MUST in the future versions of Android.
As we see, Google reports that currently is highly advisable to set default data encryption and that in future versions if it becomes mandatory . Surely Google backtracked by complaints that data encryption affected the read and write speeds , and thus the performance of the devices, which both users and manufacturers did not like too much.
Currently the Nexus 6 and 9 Nexus are the only devices that come with encryption enabled by default, and it seems to be very few, because new devices presented with Android 5.0 as the new Moto E , M9 One HTC or Samsung Galaxy S6 come without encryption enabled.
Surely Google compels the manufacturers to enable default data encryption on new devices when only affecting performance, either by using faster memory, the system F2FS files and / or processors that are able to encrypt and decrypt older speeds.
So the thing finally left untouched since Android 3.0, which is the user who decides whether or not to enable encryption of your devices from security settings.