To be honest, shutting down everything but 4G and 5G seems like a really dumb idea to me, especially in the US, where there are lot of sparsely populated areas. 2G and 3G, fine, there's no real use for them anymore, but GSM still has the best coverage and is perfectly sufficient for (emergency) calls . For 4G, more antennas would be required, which I'm sure isn't a cheaper solution.