I'm generally aware of much of this, but it suggests an interesting argument about economics, in general. Pay according to ability, "tent-pole" products (these exist in for-profit services and retail as well), etc.
The cost isn't just for the translators however - most of our stations also produce content themselves that is local, and many produce their own shows as well. Those are not small investments, but a smaller audience in a rural area means fewer people to raise support from. Our Alaska stations actually band together to help keep radio going across Alaska, though population is thinner.