@extomar: What is some evidence you can provide to support this opinion? GTA V, a single player game, broke records. It does have online components, but that is certainly not its selling point.
Do you know how expensive GTA V was to make? And that multiplayer component that outlived the game is what people are playing with as much as anything today.
Not everyone can make a game as big and expensive as GTA let alone any number of other games like Skyrim. Is a producer going to be excited about spending millions on a sword/sorcery action rpg that has a NN hour single player campaign or a sword/sorcery action rpg that is a 4 player co-op game with an aggressive advancement system that has a lot of opportunities for in game purchases? Hell just look at how much multiplayer and how much stuff is being sold in Dragon Age Inquisition.