On most European airlines, the default is seatbelt sign off unless you hit severe bumpiness. So on an 8 hour flight, you might have the seatbelt sign on for maybe an hour other than take-off and landing.
The U.S. being more litigious has led to a default of seatbelt sign on. So on my 9 hour flight from MUC to IAD on CO dba UA today, the seatbelt sign was turned off for less than an hour. Of course, that means that everyone ends up ignoring it because we are humans with human bladder capacity.
I used to think this was just pilots forgetting to turn it off, but I fly so much that I have become convinced it is policy - and bad policy at that.