Grant,
For years, tour pros and better golfers chided architects who hid even the base of the flag, precisely because it is unsettling to most. Outside this web site's "quirk lovers" I doubt many would intentionally try to hide too much of the green. And yet, it does happen.
We also try to keep upland water from flowing into bunkers, so be necessity, if you have a frontal bunker, you also have at least a small lip higher than the green to divert water around. And Leo is right, as those areas tend to build up with sand splash over time.
Side note - Lee Trevino once told me he thought even the slightest slope away from a bunker shot was weird, because he wanted help stopping the ball. Basically, 99% of greenside bunkers wouldn't fit his criteria!
Bunker visibility is also an issue, and if you want the whole bunker visible, you need to build the base at grade, not cut it in too far. The usual drill is to build a fill pad up 3-4 feet for the green so you can see that behind the bunker. Obviously, playing downhill makes all this easier, and I do find its a bit harder to put frontal bunkers in on an uphill shot to the green, and tend to push them to the side. If you can't see the putting surface playing uphill, at least its nice to have it's sides marked fairly clearly by bunkers.
Others opinions might vary, and as you say, every condition is different.