As someone who just bought the game this past weekend and has only played single-player so far, I can say that part of the reason I haven't done MP yet is that I want to learn how to play the game properly before joining a team of people I don't know that probably take the game far more seriously than I do.
It boils down to that for me. Demigod (and Dota games in general) is an unwelcoming game for new or casual players in the sense that not only are you punished if you screw up, I mean fairly small screwups compared to other online games--but your whole team is as well. And since stats are involved, it's not like they can just roll their eyeballs and write the game off, because their ranking etc. is now messed up by me being a noob. I can understand them hating me for being on their team if I go chasing other Demigods into towers and not run away fast enough, or not know enough about which items to buy, or picking the wrong abilities to advance.
By comparison, in a 1v1 RTS match if I play bad no biggie. Hopefully I learn something from the experience and do better next time, and my opponent get a kick from stomping a newb and a slight improvement to his stats. That's all good.
Alternatively, if you are playing with bigger teams, say in games where it is 10v10 or higher the noob effect tends to balance out more--out of 10 there is always going to be one or two--and premades are less of an issue because it gets problematic to stack a premade of 10 or more players.
Anyway if Demigod has a more dedicated singleplayer experience they would at least have that, and would have had more leeway to fine tune the multiplayer experience over time. With what Stardock has been saying, it looks like they get that and are designing Elemental: WoM in that light. Too bad it is probably too late for Demigod; there is a lot of singleplayer potential here that would have been awesome with a little imagination and interest in that direction.