For such games to work, they need direct access to the video hardware of your Mac. You can only get that through Boot Camp. The virtual machines also use a virtual video driver - it's not the same and gaming performance suffers. Both Fusion and Parallels have worked hard to improve it, and video is fine for normal productivity applications, web surfing, YouTube, etc. But not for games that demand all the resources your video hardware has - it's just not likely to work the way you want it to.
Cheers