In modern car design, function follows form. Case in point: the modern-day decklid.
For the greatest contrast, you might refer to a mid-60's car such as this 1966 Cadillac:
Then take a look at this current generation STS:
Now, I'm not saying we should go back to the humongous trunks of the 60s. But consider that my dad's friend owns a previous-generation Impala, with a huge trunk. He had purchased a lawnmower, and he wanted to load it into the trunk. He couldn't. Not because the trunk was too small, no. But the trunk opening was too small. And that's just upsetting.
There have been numerous times where I have tried to load something into the Cobalt's huge-for-its-class trunk, but the opening was simply too small. Manufacturers try to compensate by cutting the trunk lid deeper into the bumper of the car (hence some very interesting designs in this decade: the Grand Prix, the Altima, the-- well, just about every 3 box design).
So, screw sedans and coupes. How about a wagon? No one likes wagons anymore. How about an SUV? So, I'm going to halve my fuel economy for a bigger trunk opening? That's a great idea! Where do I sign up? A minivan? Another vehicle with the wrong stigma. How about a hatchback?
Hmm... How about a hatchback...
Hatchbacks and short wagons make up for the drastic change in trunk opening size over the past 40 years. In GM's stable alone, consider the Cheverolet Malibu MAXX. While it has less overall cargo space than the Malibu Sedan, it has that big hatch that allows for large objects to be inserted into the vehicle, such as televisions, air conditioners, and lawnmowers. And subjectively speaking, the MAXX also looks better than the Malibu. Also subjectively speaking, that's not saying much.
There are other more innovative designs such as the Mazda 6 Hatchback. When closed, it bears remarkable resemblance to the sedan, but with a wiper blade attached to the window. Surely this is the answer to the problem at hand? Well, maybe. But the Mazda 6 trunk is smaller than the Impala trunk, and won't fit that same lawnmower unless you can fold down the back seats. And many enthusiasts on this board don't want a hatch, for their own reasons.
So the engineering solution is to make a bigger trunk opening. But how does an engineer pass that to the design team?
Before I say anything else on the matter, I meant for this to be an open ended thread before I started writing it like an article. So I'm going to cut it off at this point to allow others to express their thoughts on my insanity.