I don't remember finding an option for enabling this. i will take a look, but that is actually a great observation, i haven't realized that they aren't able to pivot!
https://docs.unity3d.com/540/Documentation/ScriptReference/NavMeshAgent-angularS...
So looks like it's a function of speed, max accel, and angular speed. With absolute speed capped, max accel and angular speed probably aren't too concerning to set very high.
Good luck!