It's also possible this gets submerged in other tasks on the flight deck.

On a recent flight, the seat belt sign stayed on well after arriving at the gate. I was pretty impressed, nobody got up for at least a couple of minutes!

Eventually, though the momentum shifted and everybody stood up. Since I was one of the first out, I stuck my head into the cockpit and said "Seat Belt Sign is still on", the Captain muttered an oath and immediately reached over his head. to turn it off.

All the best, James