Sonic Unleashed has been brought to PC thanks to intrepid modders. My first question was "why?" but now it's "how?" as the game doesn't exist on the PC format. it's simple: they modded Sonic Generations to make it run silly.

As with other Sonic games from that generation, Unleashed never recieved a PC port. The go-to way to "play" it for years was the Unleashed Project, an incredible mod that recreated the main acts of the game within Sonic Generations.