Just look at GTA 5 on PC.
Already it is at 1/4 of players as when it was first released.
And that was one of the most anticipated games in a long time.
The fact is there are just TOO MANY games out there so the population per game is incredibly thinned out.
If Star Citizen is primarily single player then it won't matter so much.
But primarily multiplayer based games, such as the new Dirty Bomb, they are just destined to fail at this point. There is a major Attention Deficit Disorder issue with PC gaming, a lot of people consider a game to be old once it's out of beta.
Look at all these survivalist games on Steam. DayZ, Rust, etc etc... they are all dying. And they aren't even out of Beta.
I can see your point regarding certain types of genres, just not PC gaming in general. Recent single player PC gaming has exploded with the likes of Pillars of Eternity, Cities Skylines, Divinity Original Sin, and Witcher 3.
At its core, GTAV is the same GTA that we've seen time and time again, except with better graphics. In my view, GTAV is an artifact of the "Call of Duty" era where the same game is repackaged ad nauseum. I'm not picking on console gamers, but for whatever reason they are more inclined to perpetuate that cycle by gobbling up millions of units.
In regards to games like DayZ and Rust, games that go into early release aren't any less buggy than games that don't. They are there to bring money into the developer and actually are risky because mediocre games will be exposed and interest will wane. They are dying because they simply aren't that good, not because of gamer "ADD" as you would describe it. The post apocalyptic genre in general isn't as strong as it once was. There will always be demand for well made games, but demand isn't such that we will forgive mediocre design.
In short, I believe you are incorrect in your assessment of the state of PC gaming as a whole. A large selection of games is a symptom of healthy demand. That said, you do have a point about the state of games that are designed as online only products. I think interest is less, especially in the face of huge single player releases showing up.