A bunch of things in newer generations reduced the costs for operators (higher terminal density meant less need to buy up new sites for base stations, etc). An

A bunch of things in newer generations reduced the costs for operators (higher terminal density meant less need to buy up new sites for base stations, etc). Another part is gross simplification of many protocol aspects and moving of "central office" to data center. 5G for example AFAIK makes mandatory what has been slowly been introduced since UMTS, that is a full IP telephony stack. It was already pushed hard on LTE but was optional (and later sold to users as VoLTE). Among other things it allows all phones to easily use "WiFi calling" or connecting anything to the network so long as you can route an IPsec connection to provider edge. (anyone remembers ugly special SMS Sending cards full of sim carriers, used by paid text suppliers?)