Resistance: Fall of Man sold over 4 million copies as far as I'm aware of, and I'm sure most people bought it for the single-player. The Uncharted series and The Last of Us are popular for their single-player campaigns, and multiplayer is seen as a bonus in those games. The Batman Arkham series sold very well, and they're single-player games (Origins have multiplayer, but not many people play it last time I played it). The recent Witcher 3, single-player game, sold 6 million copes.
While I can respect your thoughts and opinion, It's rather bias to just state that single-player games are dying, when it isn't the case. Sure, there may be around 500,000 people playing CS:GO, but Skyrim still has many people playing it and with the upcoming Fallout 4, what you had stated would only be seen as false even further to many.
