Basically ‘duty cycle’…same reason electric heaters all put out 1500W but ones for larger rooms are ‘larger’. Big or small, they both put out 1500W, but the small ones can only do it for a few minutes at a time before having to cool off, while the larger ones can run for longer and heat up a big room more quickly.
For sure, anyone who has seen some of the videos of drink carts and luggage bouncing off the cabin ceilings during crazy turbulence shouldn’t have any questions about the utility of seatbelts in less than catastrophic events… Which of course is the goal even in ‘crash’ landings. There are crashes where seatbelts would obviously be worthless, but in anything short of that, you’ll be happy that you weren’t in a box with 300 human shaped dice being shaken up.