Because they are ugly, road-hogging, gas-guzzling, unsafe, ridiculously overpriced, and completely inappropriate for suburban and commuter driving. I am astonished that people can be so deluded as to actually spend (or more likely borrow) good money on such monstrosities. Not even station-wagons can challenge the sheer awfulness of the suburban SUV. A well-designed SUV (and there aren't many of those) belongs on a safari range or a ranch. No where else.
When someone does SUV-henge (along the lines of Nebraska's Carhenge), then they will have found their true destiny.