I recall Killian and Nugent putting very little pizazz in the back of their greens, and was told the reason there are so few greens with good stuff behind them is that so few golfers ever get there.....so in essence, for most its a waste of hazard money (construction, maintenance) and an under appreciated scenic view. For architects often on a limited budget (and who isn't these days.....) its hard to argue with the basic logic, at least more than a few times per round.
Of course, if you are merely talking shaved areas, the only thing really holding that back is the normal back to front slope of greens, together perhaps with the modern trend of elevating them, and adding in pretty steep slopes to save fill back there. At Medinah No. 3, hole 1, Rees wanted a chipping area and had to elevate it several feet to make the chipping work out right. That always looked a little forced to me, and many other existing greens would be in the same boat.
As to the reverse theory, it may be true at TOC. That said, how many architects these days even put much contour in the front approach areas of greens? With the aerial game, that art has largely been lost.
George Thomas wrote the most about the backs of greens, I think. His theory was that shaved grass especially on long approaches was easier to recover from, and should be used because a shot that goes a bit long is aggressive and a better shot than one that comes up short. Thus, deep rough and an uphill pitch from behind the typical green might discourage aggressive play.
Ross was supposedly famous for his lack of back hazards, although I think he built more than that strict stereotype said.