I think that one thing that makes present day courses harder is that most modern courses are built around housing developments. Out of bounds comes into play more frequently, and scores can add up quick. Sometimes there is a long drive between holes, this kills one rhythm and because the houses dictate the routing vs the land, you sometimes get some hideous, very difficult holes.
People seem to like gimmicry, and that shows a lot today compared to the minimalist designs of the past. These gimmicks just make the game harder and rounds longer.
I started playing golf in the mid 70's and I remember most people playing from the white tees. 5800-6200 yards was the norm. Now, no one seems to play from the whites, 6200 yards is considered "sissy". I see so many players out there hitting from 6600 yards plus, they have no business there. So courses that might play fair from the whites for the average golfer, become harder than they need to.
I have played all over the world, and nothing beats the minimalist designs of old and some today. If we had less gimmicks, golf courses would be cheaper to build and maintain, green fees would be lower, and the industry would not be in the slump it is today.
A course with a slope of 110 gives a hakcer the chance to get a few pars and not lose a load of balls. I don't know why easy courses are not built anymore, is it all about ego? Most courses are 130+, that is very difficult for anyone who is new to the game or the casual golfer.