The real kicker is the last line. T-mobile can software upgrade its LTE equipment to 5G: > The partnership with Ericsson means that T-Mobile’s already installed base of Ericsson Radio System radios will be able to run 5G NR with a remote software installation.
A firmware update to make existing hardware have a longer lifespan and help Ericsson to retain their clients was likely the only out here. If Ericsson had the new chips they were planning on, this firmware update would be much more expensive and less probable to actually see carriers taking them up on it.