Bill McBride,
I'm not so sure that it's a conscious decision.
My GUESS is that the fellows running the equipment give the very deep and precipitous bunkers a wider berth when mowing out of fear and prudence. I think that this is combined with the buffer factor that has gained popularity in the US, that some last ditch feature should save the golfer from a dire fate.
Over time, the condition, gradually gets worse and worse, without anybody noticing it until it's out of hand.
But, to rectify it, takes a one big effort, which would be very noticeable, and I think many resist fixing it because they don't like change in big chunks, and their frame of reference is that it's always been there, as if the architect intended it.
But, eternal vigilance is the price of greatness, and Superintendents and Green Chairman, if they are attentive to the golf course, should watch out for and fix this condition if it exists.
Most people never notice it.
But, on the left green side bunker on the 13th hole at GCGC you can really see how the fairway lines have been moved to accomodate this feature. Unfortunately, the condition is pervasive.