Kinda easy to do when you are the only racing game out there and the other game is having a identity crisis.
Maybe.. this generation has offered many new Racing games and to Turn 10's credit, both there racing series are delivering and there not just flukes or out of the blue one hit wonders. Mario Kart 8 did beat FM7 or FM6 one year I cannot remember which one to be exact and Rocket League beat FH2 or something like that, but 4 out of 6 RGOTY games is very impressive in one generation and that goes unnoticed by the majority.
Next gen will be different, GT and PC will be better games and so will other racers. It be interesting to see how Forza continues to maintain there dominance next gen.