The US FCC decided, on their own, that this was not an important problem, compared (most likely) to the amount of money to be made building out 5G.
I dislike Ajit Pai as much as the next person and wish he had heeded NASA's request to delay the 5G role out. That said, it's not a forgone conclusion that 5G will significantly interfere with let alone eliminate the ability of radio spectrometers on weather satellites to measure water vapor using the 23.8 GHz band.
The new FCC UMFUS regulations that govern 5G require require signals to use a set of frequencies all of which are greater than 24 GHz.
That said, of course NASA is concerned about malfunctioning 5G transmitters leaking into the 23.8 GHz spectrum. Hopefully out-of-band emissions don't become a problem. It's the FCC's job to ensure that it doesn't, and the lack of carefulness so far in the process doesn't inspire confidence.
There is some possibility that the 5G systems could actually be used to measure some atmospheric properties, similar to the way Navstar GPS L1/L2 signals are analyzed, but since that isn't a requirement of the 5G spec/regulations, it won't be baked in.
When you say 5G, do you mean actual 5G in general or are you talking about mmWave (FR2, sometimes called 5G high band vs low band)? It's been frustrating having these things get mixed up, because the 5G standard has a lot of improvements aimed at more efficient spectrum utilization, further reduced latency, and other changes across a unified massive range of frequencies compared to previous standards. It should be quite useful therefore for existing spectrum as well, just as WiFi 6 brings improvements to 2.4 GHz utilization. T-Mobile for example has said its initial plans for 5G include using its 600 MHz spectrum, with mid-band and mmWave going to certain urban areas.
For whatever reason though most media and even tech people often incorrectly use 5G interchangeably with mmWave, and since 5G itself has plenty of changes it's not always clear what aspects someone is worried about. I assume in this case it's specific frequency blocks of mmWave that would be the interference concern, but I honestly don't know enough about the weather sources to be sure of that vs some other change to modulation causing more out of band interference or something like that.