Android Button default state

Why is Button's default behaviour state_activated="false"?
Using this selector it never reaches the last row, it stays on the second line:
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@color/colorPrimary" android:state_enabled="false"/>
<item android:drawable="@color/colorPrimaryDark" android:state_activated="false"/>
<item android:drawable="@color/colorAccent"/>

Let's say this selector is shared amongst Buttons and some layouts which pose as a button, but in layout's case, setActivated(false) is needed to change the background.

The default state of activated is false for all Views. The easiest way to understand why is to consider the case of tabs over a ViewPager.
The activated tab is the one which represents the visible page - it doesn't make sense for multiple tabs to be activated at the same time.
I mentioned in my blog post that activated could be described as "selected" to someone that didn't know the terms Android used.