When iOS debuted in 2014, Google quickly announced that it would make full disk encryption mandatory under Android 5.0, codenamed Lollipop — and then backed off that claim once it became clear that a significant number of Android devices, including its own Nexus handsets, took huge performance hits in Lollipop with FDE enabled.
Instead of being mandatory, FDE became “strongly recommended” (Apple pushed ahead with full encryption in iOS 8 and 9, but it has more control over the entire product stack). Now, with Marshmallow, Google is mandating full disk encryption, provided the hardware meets certain minimum standards.