Why does placing the heavier trailer in the rear position of a doubles combination increase rollover risk?

49 CFR 383.115(b) ("Proper placement of heaviest trailer") and (c) ("Handling and stability characteristics ... rollover in steady turns"); AAMVA CDL Manual Section 7.1.1 "Prevent Trailer from Rolling Over" and 7.1.2 "Beware of the Crack-the-Whip Effect,"

Understanding the 'why' behind the placement rule, not just the rule itself, helps on scenario-style test questions and makes the rule easier to remember and apply correctly in the field instead of just memorizing an isolated fact.