It's configured like this in case you do actually want to lock the car normally but leave the windows / sunroof open. If you then want full closure you then just continue holding the button down
Another little trick with the remote that you may not know about is that if you do a single press on the lock button it locks the car and sets the deadlocks. However if you double-press the lock button it will lock the car but release the deadlock (car will still be locked just with no deadlock) and the interior volumetric sensors will also be disabled at the same time (useful if you have a pet you need to leave in the car for a short time while you pop into the
shop).
With deadlocks set it prevents the car being opened from the handles inside when the car (i.e. so a thief can't smash the window then just open the door from the inside). With deadlocks released, the car can be opened from the inside handles even when locked.