Reasons from my experience:
1) afore mentioned environmental
2) afore mentioned members not wanting tolose balls/strokes
3) seniors/ladies who do not/can not hit down aon a ball in short grass want to 'scoop' it out of longer grass. Most bank areas are sloping down to the water, so a downslope, over water, from tight fairway is pretty much the kiss of death to the higher handicaper.
4) supers who bemoan 'I have no where to turn my mower around
5) too much wear and tear too close to the edge from #4
6) as water tends to drain toward a stream, this area stays wetter longer (see #1,3,4,5)
Personally, I found that putting a couple of those dreaded catch basins in before the bank allows the fairway to be brought much closer. I still prefer, fro deliniation purposes, to leave about 12' to the top of bank. If it is a downhill hole, I might leave a bit more and put some additional catch basins in the rough just before the bank. In addition to solving some drainage issues, the reverse grading of the basins will slow a ball, not make all shots hit from a downslope, while still afford some randomnessin the final result due to the rub of the green.