That's mostly because I think (as they also must) that "making maps" is something that everyone does (in our heads; verbally; on the back of scrap paper; on random car-floor cardboard tacked to trailhead signs) but that few easily-accessible software tools have ever tried to facilitate digitally.
I'm interested mostly in the user-experience they've created to add our "human effects" to an "existing" map (like notes, relevant points, lines, directions). I really am drawn to it.
They're putting a lot of energy into the data-layer side of things, which I think is admirable considering the complexity, and seem to be nailing it. I'm not sure how folks will use those things, since I don't think our mental maps often require additional data.
I'll also add that their curated set of example uses is an excellent model for how to show people how to use a product that they might otherwise have no idea what to do with.