Last year, Google made headlines when it revealed that its next
version of Android would require full-disk encryption on all new
phones. Older versions of Android had supported optional disk
encryption, but Android 5.0 Lollipop would make it a standard
But we’re starting to see new Lollipop phones from Google’s
partners, and they aren’t encrypted by default, contradicting
Google’s previous statements. At some point between the original
announcement in September of 2014 and the publication of the
Android 5.0 hardware requirements in January of 2015, Google
apparently decided to relax the requirement, pushing it off to
some future version of Android.
Ars’s guess as to why is performance, which seems likely. It just shows how hard it is for Google to move the state of the art forward with Android — everything takes a year, or longer, before hitting the market.