Some other factors are bunkers are a different color/texture from grass and hence standout visually. Therefore, they are used to also add visual complexity to panorama. Architects also use them to define strategy. A grass bunker just doesn't impart the same degree of attention that one fill with sand does.
Here's 2 examples:
I just did a remodel where the course had to stay open during construction. This led to much interaction with the memebers. The biggest subject - hands down - was sand bunkers. On one hole, a straight away short 4 (about 360) had a pot bunker about 210 on the left. It only affected seniors and women. Everyone else just blew it by. I grassed it in and replaced it with one 260 on the right. As I was carving in the new bunker, I had to stop and let a couple of old guys hit their second shots (from the vacinity of the old bunker). Then they drove past, turned around and said - with dismay bordering on contempt - "you aren't putting a bunker in there are you?" I had to bit my tongue. I wanted to reply "what do you care - you're never going to be in it" but had to be politically correct and just nod.
On another hole, I built a entire new green complex 80 yards beyond the present green. The green is rather large - over 11,000 sf and is really 2 greens in one - side by side. it has a narrow throat leading to the left green/side and the right half has a deep 8' horizontal bunker across the front of it. The rear has multiple hollows in case one goes long (but these are not visable from the fairway). I did not put the sand in for about 1/2 year as I needed to take out the old green first before I could see what I could see of the bunker (I also over dug it by about 18" to make room for the spoils when I did cut the sandline in).
You would not believe the rumors flying about whether it was going to be sand or grass. The high handicappers kept lobbying for grass while some of the better golfers lobbied for sand. It was a nice distraction, so I let them stew about it (athough the club president knew that it sand on the plan and would be sand upon final completion).
Also, the architect really needs to be more hands on when creating landforms like bumps/hollows/slopes/ridges and the like. More so than 90%of creatng a sand bunker. Why? Because most contractors just don't have the eye or feel to make them look and play correctly. sand bunkers are more repetitious and can be tweeked at the end by the architect. Plus earthforms need to be shaped in subgrade and then topsoiled. If, after topsoil, they don't work, you have to re-strip off the topsoil and reshape the subgrade. Each time you handle topsoil, you lose about 20% of it. Plus it's hard to convey on paper at 1"=100' - 2' CI. Even at 1"=50' and 1' CI you need a shaper with lots of experience and one who's insync with you.
I did a job with Landscapes in Souix Falls where I wanted the landforms more complex than the plans showed. The super complained that if that's what I wanted, that's what should be one the plans (although he knew the plans @ 1"=100' were only to get it close). So when the clubhouse plans required the practice green area to be moved, I drew it with all the ins & outs, ups & downs to satisfy him. Guess what? He came back with "How dow you expect me to stake this? There won't be enough space to get a dozer between the stakes". Damned if you do, damned if you don't.
Then there is the practical example ofpresentation posed by Mike N. Just look at the entries in the Armchair Architect contest. If it don't "look" like a golf course, you don't have a good chanceof getting the commission. You can always take them out in the field - they are actually a good trading item to use when horse-trading CO's with the contractor.