Find my iPhone unknowingly turned off
In order to disable &quot;Find My iPhone&quot; you'll need to know both the AppleID password as well as any device pass code. It cannot really be done accidentally by just tapping once or by someone that lent your device for a minute to call someone.
There's also nothing in iOS that automatically disables &quot;Find My iPhone&quot; for you.
However, contrary to what you write, it is actually disabled by default. So most probably you have never enabled it.