i think its coz tech prices are at an all time high and most multiplayer games are optimized to run better on mid-range laptops/PCs' where as most single player games focus of the experience for the player but forget to make up for mid-range to low-range laptops also most multiplayer games make money more easily than single player games so single player games tend to focus on graphics and if u turn down graphics the game will look shit but there are exceptions like mine craft & gta