Because there is no native PC version, players use community-developed software to run the game on Windows 10: Forza Horizon Full PC Emulation Guide | Xenia
If you want a true, native, native Windows 10 Forza Horizon experience, look to the official sequels. All of these run flawlessly on Windows 10 and support high resolutions, ultrawide monitors, and 60+ FPS. Forza Horizon 2 Pc Download Windows 10