Multiplayer is more popular than Single Player
I find this very hard to believe now, and I find it very hard to believe that this will ever be the case outside of some kind of paradigm shift to how people with full time jobs spend their free time.
The very nature of Grand Strategy makes it difficult to play in multiplayer mode.
Things that keep me(and I imagine most others) from playing Grand Strategy multiplayer:
A) It's hard to find people on the same work/family schedule as you.
B) It's hard to find people who want the same house rules as you.
C) Time investment
D) The internet is infested with trolls and spoil sports which makes Pick-up groups(in grand strategy) almost pointless.
So, while I'm happy for those of you who are unaffected by the above problems, the fact is that the transaction costs for multiplayer grand strategy are very very high. This is what makes single player very attractive to people that have a family and full time jobs. We can pick it up, play for a few minutes, save rinse and repeat.