If I remember correctly, the novel was concerned with a generation ship travelling to a distant star. This is not the same as space habitats in a solar system where there are plenty of sources and sinks for all materials involved in the maintenance of a habitat.

I think he modeled his habitats as large ecosystems as well in the novel. That's not strictly necessary and would simplify the design a lot.

Also, it was a fictional story so not the best source for information. Which is kind of proving my point about sci-fi messing up everyone's conception of what the future could hold.