There's just so many cell towers compared to radio broadcast stations. The very nature of the frequencies demand it. You would need ~$1m upgrades to every tower to retrofit with generators capable of lasting more than a week.
I think it would have a huge impact on monthly bills for cell service. Likely one that the general subscriber would not appreciate given the rarity of a knockout event.
In these more rural areas where it's more likely for trees to take out the power supply and restoration takes a long time, adding solar and battery backup would be much cheaper, and might even make it's cost back in reduced power cost during non-emergency times.
I think it would have a huge impact on monthly bills for cell service. Likely one that the general subscriber would not appreciate given the rarity of a knockout event.