To use the emergency alert system, your phone must be connected to the cellular network. That works great for things like tornado warnings or Amber alerts, etc. But two weeks into a disaster, when all the cell towers have been dead for well over a week, that gets a lot more difficult. And the emergency alert system is for short messages - i.e. "Tornado! Take cover!" or "Look for this license number...". They don't work well for long lists of water distribution locations and updated stock, instructions for leaving the area with bus schedules, etc. It is a lot easier to provide emergency power to one radio station operating independently than to a thousand cellular towers, which are all connected by fiber lines that will be severed when an earthquake hits. So for immediate duck and cover type warnings, the existing cellular system works great. For coordinating large-scale multiple-week disaster efforts, they fall apart quickly. That's why emergency response teams have phones and connected devices, but also have complete stand-alone systems like VHF radios.