Confusion about Diagnosing Problems with a Commutated (Brushed) Motor
In a two-brush motor, the rotor is wound with all of the motor coils carrying current in two parallel paths. That more fully utilizes all of the windings than would each pair of commutator segments connect to one coil. In addition, I believe that reduces the commutator sparking because each segment transition only changes the current path by a small amount rather than shutting off the current in one path and turning it on in another.

Answers in the other EE stack exchange question linked in this question explain the contributions of winding segments with various orientations with respect to the stator.