I change down the box when approaching cyclists when I don't immediately have enough room to pass them. Of course I can't be sure they aren't wearing headphones or fiddling with their phones, as with pedestrians.
I'm of the generation that was taught to change down as you slow down, and the generation that doesn't wear headphones, or constantly check phones. Most drivers don't change down, and indeed prefer not to, so they pass in top gear, without indicating their presence, and usually too close.