I would also add "sex appeal" to the reason SUVs took off. The "active lifestyle" became popular with Americans around this time as well. SUVs were seen as sexier alternatives to station wagons. After all, an SUV is just a 4WD station wagon.
But actually, I guess that explanation doesn't hold much water either. The "health craze" probably took off in the 60's and was definitely strong by the 80's.
Guess the tax breaks for SUVs (they are classed as "light trucks" and therefore offer many tax loopholes) may be another major driver of the trend.