Pat,
Yes, I agree with your premise and its a great question! However, I recently fell out of competition for a major redo at a prestigious club for answering this question honestly - "Mr. Brauer, don't you think I should be able to reach a par 5 in two shots just as easily from the fairway bunker as I would from the middle of the fairway?"
I just finished an article about course length for Golf Course News. The sad fact is, as you know, that less than 1% of golfers benefit from the ProvI. No one else hits it further. In fact, I have recently seen several courses of the 1970's era which ushered in the 7000/6600/6400/5400 yard standard, now remodel tees because the course is not long enough from the back tees, but also, way too long and difficult from all the rest of the tees for members to play it comfortably. I think the ideal split for todays golf is 7500/6600/6000/5400/4500.
So, the question is, are we not aware, or are we simply choosing to design courses in similar ways, because for most golfers, the game is still too hard and deep fw bunkers like you suggest only make it harder? From the question above, I don't think tastes have changed towards deeper bunkers that much.
As I once related here, as a 12 year old kid loving gca, my first design philosophy, never with a real chance to be implemented was to use few bunkers, but make the ones I did use really mean something - i.e., be crap your pants deep. Somewhere along the line, I fell in line, although I do try to vary depth. I think its still fine with most people to have one or two really deep conversation piece bunkers, but most people would limit it to that, and some would limit then altogether.