To get monthly subs out of the way, you would need to charge monthly subscriptions in order to maintain those servers. Servers aren't free to host and maintaining them isn't either, or churning out updates for the games. Please understand why it's necessary before hating on it.
I love it how people point out Company of Heroes and World in Conflict to be superior to the "spam-fest" and "click-fest" of Starcraft, even though those two games practically have their own imbalances and "spam-fests" among their "constant tactical gameplay", nothing like a little Pio-spam and mass scout helicopters and mass medium/heavy choppers to change some opinions around.
To address your question, it goes like this, if a sequel to a game you played and thought was good was coming out, wouldn't you be more inclined to buy it? Wouldn't you also tell your friends this good game that you played is having a sequel and how it will be better than its predecessor?
The reason Starcraft 2 is popular is because of the competitive nature (And a nation to support that) behind it and the fanbase it gathered over the years. The fact that a 1998 game survived more than 10 years and still having people play it. The competitive part of it is also due to the company supporting it and patching what is considered really imbalanced, while games like World in Conflict and Company of Heroes doesn't have this kind of support and is left with certain imbalances. Having more than a certain number of imbalances, and you'll have something like Command and Conquer, which is practically dead if not rotting away, and you don't see that game being more popular than Company of Heroes because of that.
Innovation isn't equal to a game's quality or how good it is, the FPS genre is a decent example of this, it's like saying Team Fortress 2 should innovate, so it should have a cover system, iron sights and other stuff. Team Fortress 2 is essentially the same game as its predecessors, the only real difference is the fact it's more balanced and it has a few new features. Another example would be Counter-Strike Source, people still play that and people don't complain about lack of innovation in that game (And more people play that than TF2 itself).