I recall the old Cornish and Graves books wrote and diagrammed that fw bunkers ought to be built above grade, and my mentors felt the same, so I had the impression that style developed in the 50's as part of the streamline era.
However, the reasons make sense from many points of view -
Raised bunkers are visible, sunken bunker are not,
Raised bunkers are easier to drain and sunken bunkers are harder to drain (impossible in some cases)
Raised bunkers do reject balls, whereas sunken bunkers can collect them, so where you are really looking for factory golf (yes, it is a design criteria for many clients) it may limit the amount of time devoted to getting out of fw bunkers, one of the hardest shots in golf for typical ams.
Raised bunkers used fill that came from irrigation lakes, more practical than wasting localized spoils around a smaller scale bunker, so oddly, the rise of irrigation also raised a lot of bunkers.....
Tying in long slopes eased mowing when mechanical mowers came along (of course, horses and gang mowers also worked better on long flowing slopes, too)
Not surprised that after 60 years of that style, that many are sick of it, and looking to try something new!
I would ask Ryan if he was against the raising, tying of slopes, etc., as much as he just likes the smaller scale and randomness of older bunkers?