For me, it's the settings. I can make the game play exactly how I want. My GTX 1070 may not be as powerful as the Xbox One X, but I can still turn it into a 1440p 60 ultra settings card rather than trying to force 4k on everything. Also, PC lets me use any control options I want.
There's also mods and exclusives, and the fact that it's convenient to have a machine right there that can do everything besides gaming as well.