The point has been made that, if all the cars in the game are ones and zeros, why does it matter if VGT cars are in the game..?
To which, I might reply, then why any real cars at all? Why any tracks on the surface of the planet? Why gravity? Why any physical forces? Why no forward facing photon torpedoes? Why no power-ups? Why no Italian plumbers in karts?
The answer would be, because it's Gran Turismo. Not Pod Racer, not Mario Kart, not Wipeout. Once upon a time, the 'imaginary' cars in GT were a minuscule fraction of the total car list, and based on cars that existed. Nowadays, they are an unavoidable cancer on the game. You can't even specify (in Arcade or Campaign) that you don't wish to race imaginary cars. Immersion breaking at best, pointless at worst.