Because EA is evil, that's why. Kidding! See, EA has the license for Porsche cars, thus, making them available only via a sub-licensing deal. The cars did appear in Forza 3, and featured RUFs, which are tuned, unmarked Porsches.

Leave it to Porsche to see the steering wheels of Formula One as just a starting point for the controls of its 911 GT3 R Hybrid racer — a Porsche with a flywheel system so awesome it's designed to kill you by stopping your heart. Somewhere in Stuttgart, there's a Porsche engineer building Joerg Bergmeister an extra…