YBitching on forums seems to be the only viable communication channel, hoping that the devs of the games come aware about the negative feedback that otherwise didn't reach them from the suits.
I don't think all the bitching in the world won't change a thing, unfortunately, as money talks way, way louder, even directly to the developers. To phrase it differently, if something designed in a specific way sells like hotcakes, it can't be bad.
CivIV didn't sell bad either, and we have much reliable numbers because much of these sales took place in a time where they couldn't be tracked with Steam, but I think it's safe to assume Civ5 sold better.
And it's no wonder, either. I keep using the phrase "Civ5 is a civ game for people that don't (really) like Civ games (anymore)". It's a very "gamey" game that's way easier to just derp around in for a couple of turns without investing too much effort.
Minor errors you might make here don't sink your game as they might have done in Civ4 (at least on higher difficulties) since the Civ5 AI is so horrible at playing the game.
And the changes that were required to make 1UPT work at all in a global strategy game (less cities, less production, fewer units) allow for a quicker playing pace as well...
To me, a huge indicator is what this thread is about - the major mods.
Look at Civ4's modding community and the sheer amount of total conversions it developed.
And what's there for Civ5? Almost nothing of note.
The SDK has been out for years (after they released it years later than they had promised to), so what's stopping people?
I think the majority of Civ5 players are those "let's derp around for a few hours" players.
The REAL fans, that loved to minmax their play, explore the possibilities, disassemble the game mechanics to reassemble them in different ways, because they really really liked Civ, those guys don't play/like Civ5. So no mods are made, because there are too few people REALLY invested in Civ5.
But maybe that's all a conspiracy theory. Does someone have a better explanation?