I can only speak for this gilded shithole country I live in, but there is likely some technical or regulatory reason they have to keep older systems online, I will give you a couple of examples - I used to do work for a hospital, they often had to connect and collect data from the state for benefits and stuff, and we had to keep a PC with a dial-up modem running up until around 2016 or so because it was the only way they could connect to the state's databases...also, there is a law that all mobile phones have to put all emergency/911 calls through, even if there is no service active...an older phone might not have a radio that connects to modern cell networks so maybe the older ones still need to exist, but anyway no do what you gotta