If the antenna isn't pointed at us, it can't hear the commands we send.

We do have to be able to tell it to point the antenna away from Earth sometimes... to point sensors at a target of interest or to align thrusters in a certain direction for a maneuver. We don't need to do these things much anymore, but the ability was critical during planetary flybys.

If we point it away in purpose, we also tell it to point back at Earth when it finishes what it's doing.

We don't tell it to automatically reset the orientation more often because that would waste fuel. When it runs out of fuel, it has no way to maintain the antenna orientation and we loose contact forever.