Its not insane when you consider any number of factors, starting with the fact that Americans are BIG. As a large person myself (although not overweight), I'm here to tell you that what a 120 pound 5'6" person finds comfortable frequently is painful for me.
Second, I spend upwards of 2+ hours a day sitting my my car, spending a couple grand extra a year for a seat that is 6" wider, doesn't require me to have the flexibility of a 15 year old doing a deep knee bend every-time I get in/out of my car, and allows me to sit upright rather than tilting the seat back into the second row is well worth it.
Third, while there are some SUV's and maybe minivans that qualify on the comfort front, they either tend to be less efficient, cost more, or have social stigma associated with them.
Sure if I had two vehicles, I might be able to get away with driving the truck on the weekend or when I actually need it, but the convenience of being able to throw a bike, kayak, lawn mower, TV, piece of plywood/drywall/2x4/etc in the back when I need to is worth it. Plus, I tow something maybe once a year, but again, if you only have 1 vehicle.. The two vehicle argument might make more sense, if there was space and insurance/taxes/etc were per person rather than per vehicle.
Finally, part of the problem is the American car market. Sedan seems to frequently translate to econobox. In Europe a basic car is smaller, but somehow frequently seems to have far more leg and headroom than a similar American car. This space problem seems to extend from the econoboxes in the US to the luxury car market as well. Apparently in the US, taking an econobox, putting leather and a bigger engine in while leaving the chassis/etc the same (or streamlining it and making it even smaller as honda/acura seems to do) is common. The result is that if your bigger than average, you likely don't fit in something that isn't a SUV/Truck.