It is all about the fear brought about by the " punishment culture " of the Koreans. Snooping by management via AIMS and foqa monitoring which at the minimum means a nasty e-message from the chiefs or maybe tea + bickies with the chiefs. Turbulence can easily cause speed excursion beyond the amber or red speed bands. This excursions are recorded in AIMS and are used by the ever diabolical foqa people to humiliate pilots.
Some managements are easy with such speed excursions( as long as they are less than 20 kts beyond limit ) but some just come down hard on the " offending " pilots. So most take the obvious way out and reduce speed to avoid speed excursions.