I would also agree with Jeff that that is a very blanket statement. It all depends on the designer. I can't really comment on Tom Doak and the other naturalist designers, but Pete Dye seems to have gone for small and shallow bunkers, at least at PGA Golf Club. While Fazio works with deep bunkers. So it is not blanket deep bunkers on modern courses. Not to mention, Wilmington Golf Course, which is profiled on this site, has several deep bunkers, one that is like 8 feet deep. So, this is not a totally modern idea.