Really. Since when do all modern games these days need Multiplayer to be a success? Origins was perfect the way it was. It did not need Multiplayer to get to where it was in 09 where it was one of the best games of the year. And really....when you make a MP game you invite all sorts of toxic individuals into the game. From those who do nothing more than attempt to lord their skills over you telling you how to play and come the simple trolls who go out of the way to ruin the experience. The game will be better off for not bringing in Multiplayer. Sometimes it seems like you hinge the success of the game as a whole on a feature the majority of players don't care about when it comes to the genre.
I look at MP as an additional option to enjoying my game; just like how others enjoy the option to play as multiple races for the PC, or the multiple options of LI, or the multiple options in terms of weapon and armor customization for the player and their companions. More options in a game is always a good thing IMO.
Now in my time as a gamer, I have never seen a video game made worse by the inclusion of MP. Oh I have encountered bad MP in the past; namely pay2win MP, or an unbalanced mess of competitive only MP full of glitchers and cheaters; but I have never played a title that became less because of the additional feature.
There have even been times when MP is actually a saving grace for a game with a rather lack luster plot. For example the video game Conflict: Desert Storm has a very generic "Soldier story" and would have faded into obscurity among the countless other war titles I have seen, if not for the fact that the co-operative campaign that had one player being held in a POW camp; being tortured/beaten to near death, while the other had to go mount a rescue operation, as the opening mission. Or the Lucasarts game: Gladius; a rather hum-drum story about an elder god of death coming to threaten a not-Roman civilization, oh and also gladiator fights in arenas. But the ability to play the game with drop in/drop out co-op, and have the other players get to play as the other gladiators and creatures in the party (my personal favorite being the walking skeleton of the Undead Summoner) really made it one of my favorite original Xbox/Gamecube titles.
It probably has to do with me growing up with two brothers as into video games as much as me, but having the option to play MP; especially co-op MP; can only bring more enjoyment out of a game IMO.