Sean,
No doubt that the drive for tougher courses, which seems to have been there in most of American golf history. There was CBM's quest for a world class course, RTJ at Oakland Hills and others, the GD rankings focused on hard, and of course, the CCFAD movement that tried to make muni courses into more championship tests. The drive for length also contributes in that shorter length might make up for harder courses.
Maybe that drive has peaked at least for a while. No doubt that three or four sets of tees work better when the back tees are closer to 6800 rather than 7500. (I wonder how many courses are really that long, but thats another issue)
That said, as a designer, form follows function. So, to start, I set a goal of most if not all players being able to play golf the way intended, such as hitting par 4's in two, so that they enjoy the game. No one has answered the question yet of why the 99% of golfers who pay the bills shouldn't enjoy the game that way, and I doubt anyone really can give a good answer.
With that as a design goal, I need multiple tees at 60/70/80 and 90% of the longest hitters, because the math cannot be overcome. A 130 yard driver cannot have par 4's over about 290 yards and reach them in two shots. That said, I do find it impractical to use the Barney Adams method of an 8 iron for Tiger is an 8 iron for Aunt Sally. I think keeping the approach shots to any kind of iron, rather than three full shots on a par 4 is a big step forward.
Of course, I make exceptions for topo, hazards, and other individual hole factors, so I might (grudingly) accept only 14 holes as reachable by those average length hitters for their class, if forced to by natural factors. I might accept par 74, knowing that a few courses with six par fives are generally well accepted. Where I have introduced shorter tees, women have said they really liked them, and it made golf more fun.
To be honest, its not lazy design. I put more thought than ever in it. What's been lazy design is architects never really considering the needs of the average player. Simply slapping a forward tee somewhere up front didn't really cut it.
As to the length equals marketing argument, I can agree, and posted a thread on it recently. That said, most businesses don't want to be the trend setter of ignoring those back tees, which shoud be only a rumor to 99.9% of players, but for whatever reason, they equate them with quality, even if they never set foot on them. I have tried to tell clients to eliminate the back tees used by so few.