Why does the AAMVA CDL Manual instruct drivers to steer gently and smoothly when pulling doubles or triples, rather than making quick lane changes?

49 CFR 383.115(c); AAMVA CDL Manual Section 6.1.2 "Steer Gently," p. 6-1

This explains the "why" behind the single most repeated piece of doubles/triples advice. Once a driver understands that steering inputs physically compound backward through each trailer, "steer gently" stops being a vague warning and becomes a concrete physical fact to plan around.