HOW IT WORKS

To rotate something you have to twist it.  The harder you twist the faster it rotates.  But, objects also have a property called inertia.  The more rotational inertia an object has the harder it is to twist.  In the case of the falling sticks, gravity is what is doing the twisting.  While gravity does twist the long stick harder, a long stick resists twists a lot more than a short one.  The stick with the least inertia wins.