Because cable companies pay broadcast companies to redistribute broadcast content - it's a major source of income for the broadcast companies. The cable companies said that if Aereo were allowed to get away with what they were doing then they'd do the same thing themselves.
So Aereo was screwed because _cable_ companies decided to overpay? Can you imagine if you bought a car, and then the dealership comes back to you for more money because your neighbor paid much more for the same model?
So a completely unrelated third party has a completely separate deal with content producers that has nothing to do with the legal free OTA broadcasts. Still doesn't add up.
Then tell ABC, CBS, FOX, & PBS to get off the effin airways and become cable-only. Surely there are those who would find uses for the bandwidth that would serve the community