I would disagree with the statement about Multiplayer being the only reason people play this game, I get equal enjoyment out of both sides of the camp and most I play online with feel the same.
Whilst it is nice to drive alongside mates, there is only so much roadside idiocy one can tolerate, the plethora of mods also gives people a huge choice to tailor the SP experience exactly how they want it.
Multiplayer is great but also very vanilla in its playstyle, it would be nice to see the new DLC's on it but it may well cause bedlam on the open roads.