Either way I am surprised that you think it should be left to each individual pilot or crew, as the case may be, to decide for themselves whether to disarm or not while taxiing in.
It's not left to the crew, the procedure is in the FRCs and is standard across the fleet.
What about the ground crew receiving an aircraft, not knowing if it is armed or disarmed?
Pin stowage on all types I've flown are highly visible from the ground so the ground crew will know at a distance if the seat pins are in or not.
As a side note, the seat is never referred to as being armed or disarmed. To do so would be to suggest that when 'disarmed' it's entirely safe. It is not, the explosives remain in place. The seat would only be talked about as being 'live', 'safe for parking' or 'safe for servicing'. I'm sure the armourers have further distinctions beyond 'safe for servicing' but that would involve serious specialist knowledge of the seat in question.