Part of the problem was its limited availability. Quadrasteer-equipped trucks didn't have the big-block or diesel option boat and RV pullers require. Essentially a front Dana 60 axle swapped around, the Q-steer rearend can't cope with the torque output of the larger motors; buyers were left with a choice of engine grunt or maneuverability. Not surprisingly, people who tow chose grunt. When was the last time you heard turning circle come up when guys talk about their rigs?
Another problem was lack of vehicles to drive. Pickups with four-wheel steering weren't prominent in dealer inventory, and, at the initial price ($3995), few dealers wanted them without a sold order. The price later got cut to roughly $2000, but that's still a significant percentage on a $30,000 truck. Further compounding the problem is that many RV owners tend to be traditionalists and don't embrace new technology as readily as other segments do. They're also likely to be budget-conscious (and practical) and expect a lot for their money.
Delphi, the brains behind Q-steer, also contributed--it put all its eggs in one basket and gave GM an exclusive for three years. The technology made its debut on a platform already a few years old and therefore missed the mass advertising any new model gets. It'd be great if Delphi could pitch the componentry to another manufacturer, but with Ford and Chrysler almost out of solid-axle SUVs, don't hold your breath.
Perhaps GM should've tried XUV and Quadrasteer on the Oldsmobile Bravada first--it would've made for a lot less bad news.