As
@PrincessShmoo pointed out, there are lots of sporadic moments where photo ops pop up. You can't just say to a random character in the hall "Hang on! I need to run to my room and get my camera!" They are on a schedule even when it seems they are just wandering.
Also some cruises (Alaska) are more prone to random wildlife sightings. My first cruise to Alaska (sadly NOT on
DCL) I was walking around the promenade deck early one morning and an entire pod of humpbacks went passed right next to the ship (I'm talking less than 50 yards away) . I was SOOOOOOO glad I had my camera with me to be able to capture that. If I'd had to run back to my stateroom they would have been gone by the time I got back.