Iowa is pretty flat. It's all farmland that's been plowed a million times (making trenching much easier, and a lot more opportunity for things like directional drilling/conduit drivers).

Try running cable through somewhere with harder ground/rocks, trees, mountains, swamp (Mid Atlantic, Florida, Alabama, Minnesota, etc) dealing with right-of-way, over-populated poles, etc, etc.

Then there's the connection rate. In a more populated area there would be many more final connects, which can drive the cost a lot more than running the mainline. If you run fiber across 20 miles with no connects (just point to point), there's minimal hardware infrastructure along the way. Add in needing switching for 5 communities, now you need buildings, power, termination, switching, runs to houses, etc, etc.

It's not really a good comparison.