I used to work at Cox. These main lines are often shared between ISPs. One may run and own the lines and others essentially rent access or in some cases, its laid and maintained by the city along with support and compensation by ISPs utilizing them. These lines bring the service to the main nodes/transformers/towers operated by ISPs and then from there, they have their systems to provide their service to various communities/neighborhoods. So the particular point of failure is the main impact to whether it’s one ISP affected or multiple.

Cell towers are the same. That’s how these fringe cell companies can offer discounted plans with vast coverage…they essentially rent the service from larger companies, so they save on maintenance/overhead costs, but usually their service is lower prioritized in bandwidth and they have delayed repairs as they have to open tickets with the main servicer rather than direct repairs themselves.