Here's Colt in his 1913 report:
"The banks of some of the bunkers can be easily modified, and if 'torn' out of the hills and natural undulations made, will look more natural. The sand can be added so as to give a good effect by allowing it to 'splash' up against the banks and look as if it had been blown by the wind, and the margins can be made quite irregular and rough,"
So why wasn't this approach used? Those traps on the 10th are built into natural mounds/hills and could have easily been "torn out".
Why the finicky shaping and grass down the face?
The "torn out" style was typical of Colt pre WW1. He writes the same comments on "tearing out" ridges to form bunkers at Toronto, Hamilton and Pine Valley. Fairly simple shapes, almost triangular in many cases, but rugged outlines.
And of course the 8th at St George's Hill was the ultimate torn out bunker.