> Unless you care about your phone working as a phone

Most of that is a chicken-and-egg problem. 3G was dropped because very few phones were still using it, and you could not run 3G on the same frequency as 4G/5G. If phones lasted longer, more people would've remained on 3G, so they would not have dropped it. Furthermore, 4G and 5G can share the same equipment and frequency due to Dynamic Spectrum Sharing, so there is no technical reason to quickly get rid of 4G like we wanted with 2G & 3G.