We know people are playing High Frontier. But we have reason to suspect that most people aren’t getting very far. (Nobody’s yet complained about the solar system ending at Mars, for example.)
We’re aware of some of the sticking points — for example, new players often don’t realize that they need to lay down some paths, and paint a nice mix of zones next to them, before buildings can appear. But there are probably other sticking points we haven’t thought of. High Frontier is a complex game, but we’ve been playing it so long that it all seems obvious to us (even when it isn’t!).