Why do Americans buy so many trucks?

The F-Series sold 763,402 units in 2013. It was the best selling vehicle in the US. The Silverado took 2nd place at 480,414 units (about 80k more than the Toyota Camry I think), and the RAM was at 355,673 trucks. These three vehicle models make up a little over 10% of all US auto sales for 2013. Why do we buy so many trucks?

Edit: As made evident by Raphael and my inability to read and comprehend, the sales figures were for the F-Series, Silverado and RAM, not just a particular variant (F150, RAM 1500, etc.).