In the US, I feel airlines and pilots view the seatbelt sign as a liability waiver as opposed to purely a safety item. This started in the late 90's when AA was found liable for injuries caused by turbulence because the seatbelt sign was off. So leave the seatbelt sign on then the airline can't be liable for injuries.

https://www.nytimes.com/1999/10/08/n...nt-flight.html