This.

You’d be surprised how much of a place’s physical infrastructure depends on a physical line. Automated fire alerts for high rises, security alarms, remote access for gates and doors, backup phone connections. A lot of this still uses old physical lines because it is easy to fix and highly reliable.

Now consider the infrastructure needed for specialized services like EMS, police, secure and classified buildings, federal agencies, embassies, smart traffic signals. Shutting down a network like that has massive implications for anything in society that relies on it, which is well beyond your cell phone plan.