i have been in some A330 where the crew are adamant that the arm rest in J be lifted up during takeoff and landing. So much so that it created a bit of ruckus when I once had a seat where the arm rest wouldn’t stay up and would slide down at the slightest touch, and the crew insisted that I change seats.

But i notice in my recent flights on 787 and A350, the crew couldn’t care to insist that they be lifted on takeoff and landing.

Does the practice differ by plane, if so why? Couldn’t quite comprehend the difference as they are largely the same seat occupying the same space?