Maybe you're a weirdo to the rest of the world, where drinking beer and watching people throw or kick a ball around is considered proper grownup entertainment, but definitely not here. Not everyone needs to socialize all the time. I often like to game by myself for the same reason I like to read or watch a movie by myself. I just want to enjoy my recreation without some asshole around to offer inane commentary, or to ruin my fun by acting incompetent or like a dipshit in game.

It doesn't help that multiplayer games tend to be very limited in what they can actually do in comparison to singleplayer games. Stories in them are often banal and can never offer a proper ending. Action games, shooters, and platformers often have to do away with large explorable levels and set pieces. RPGs leave you feeling weak, underpowered, and like more of a glorified delivery boy and pest exterminator rather than a proper adventurer. And strategy games always inevitably narrow down to a specific meta playstyle that discourages experimentation.