That's just it and it's only going to get worse. There simply aren't enough people like us that enjoy a deeply satisfying, immersive game to satisfy Firaxis or greedy 2K Games.
3 million in sales sounds fantastic (for cIV) but it really isn't in the big picture.
Unless we as Civ lovers stand up for what we believe in and fight for a quality game then this franchise will just get simpler and simpler.
It'll be watered down to absolutely nothing to satisfy the ADD riddled teenagers who want instant satisfaction and don't want to have to earn anything by actually thinking.
That's their target audience and the game will sink to the lowest common denominator.
I think there are plenty of people. Past sales of Civ prove it well enough. Let's avoid crying and making ourselves into an abused minority just because a flawed Civ game was released. If it wasn't Civ 5, then it would happen with Civ 6, 7, or 8. Every now and then they'll release something kind of messed up that needs a lot of work (no developer is perfect).
Secondly, if we are too small of a market, then no amount of "fighting" is going to change the economics. Also, I don't think people who didn't care much about the depth were bothered at all by previous Civs, considering they just played at a lower difficulty.
Thirdly, I have ADHD, so I don't appreciate people stereotyping those afflicted with this disorder. It's nearly more annoying than the disorder itself when some random person decides to blame things on people with ADHD. Beyond that it represents a severe lack of understanding of how ADHD works and what the people with it are like on your part -- and please don't try to back up your views with crappy anecdotal evidence that is inevitably going to be extremely biased by how your receive and notice the information.
Rather than try to pretend this is some kind of attack by greed, marketing, and the majority (or a minority in the case of people with ADHD) of the populace against you, maybe you should try a more realistic outlook. The game was rushed out the door, it wasn't tuned or polished well, and hence it lacks the enjoyable play of previous Civs. It also has one or two somewhat poorly thought out mechanics, but those could have been polished to a decent level so that they wouldn't have been too much of a burden. The game will undoubtedly get better with mods, patches, and expansions though. Civ 6 will probably be better still.
So, I guess you can take all of that into consideration, or you can act like THIS IS THE END OF GAMING AS WE KNOW IT. Your choice.