The obvious answer is "courses for horses." Deep bunkers not typically great at public or resort courses, but golf would be worse off if any design rule (i.e., shallow bunkers) were mandated across every type of course. What is perfect at Pac Dunes is inappropriate elsewhere, but then, no one travels across the country on a golf trip to play a course similar to the one they play every day.
As to the OP, I distinctly recall playing Royal Melbourne with my first wife, obviously not an easy course, and with some pretty deep bunkers, although the balls tend to roll down the hard packed slopes to a relatively easy shot from the bottom. Even with her shooting 100+ and me shooting 80+, we played three times and never took more than 2 hours and 45 minutes. And one day, we were behind a seniors ladies league!
All of this makes me wonder why the pace of play in the US is always so dang slow. Even muni's tend to take 4.5 or more hours, without deep bunkers. I would suspect, since they cover a mere 2000 SF or so, vs. 3 Acres of rough or surrounding trees or natives around the play corridor, so they can't come into play as much. Deep rough and narrow corridors are to me the bigger culprits in slow play.
Lastly, to my mind, even a muni course ought to have a hole or two with a deep bunker, as a contrast to the others. They could start to get in a golfer's mind early, sort of like the island green at TPC. If the gca goal is to make each hole unique and memorable for the player, certainly a few really difficult bunkers would make that hole memorable. And, my tendency would be to follow up a hole with either a lot of, or deep bunkers with a bunkerless hole to maximize the contrast between consecutive holes.