Because it's a bragging right to set the record with car in its stock form. That's why people like the Sports Auto times because they are a magazine that get cars like regular people and set laptime using setup that any normal owner would have.
BTW, if you guys know Porsche's history, you know they don't do special setup for these type of record attempts. One good example of this is how they supported the 918, P1, and LaFerrari comparison at Laguna Seca. Whatever they do to get the performance, they roll them into their production cars. They are sports car first, street car second. There is a big difference in engineering the car when it's approached that way compared to how cars are typically engineered.
