Because as far as I can tell, Minecraft doesn't support split-screen multiplayer no matter how big your monitor is. A 1080p monitor for a desktop PC is 23 inches diagonal, which is bigger than the bedroom TVs used for two- to four-player GoldenEye and Smash Bros. sessions in the Nintendo 64 era. So why don't more PC games support split-screen?
 The diagonal measure of a monitor is sqrt(width^2 + height^2), and for 1920x1080, this is 2203 pixels. The standard density for a desktop PC monitor is 96 dots per inch according to the CSS spec, giving 22.95 inches.