That was one of the things they realized with D2, the reason it stuck around was the multiplayer, they just got the idea that the whole thing should be multiplayer. starcraft has less of an excuse because there's no meta economy in starcraft.
And then they gimped the multiplayer to 4 player instead of 8 and made the game entirely too linear. I stopped playing after 2-3 weeks. I doubt they care though, they already suckered me out of my money.