The problem that Toyota, Chrysler, GM, et al have discovered over the past year as gas prices spiked and then the economy collapsed is that people are taking a much harder look at what they actually need. While there are a number of drivers who fit the aforementioned categories, most SUV buyers in recent years did not. Those people have increasingly decided that they don't need the size, weight and energy consumption of a big SUV. For those people a car, minivan or smaller crossover makes a lot more sense, practically and economically.
Finally if you do have an older SUV that occasionally gets used for its intended purpose, you may not want to get rid of it, especially if its paid for. As I advised a co-worker with an older Suburban, just leave it in the driveway, and use it when you need it. The market is so flooded it's not worth trying to sell. Just buy a decent used car to drive to work and shopping.