Ok, I see the issue.
>
>My question is why did they wait until 5G is about to be deployed
>rather than speaking up well before now?
Because neither the FAA nor the FCC have many technical experts left. So it takes a long, long time for technical issues to trickle up from the few technical people through all the lawyers up to the top.
European countries dealt with this quickly and efficiently.
And the honest truth is that for modern radar altimeters this isn't a problem. But there are plenty of planes out there flying whose radar altimeter receiver is just a horn and a diode detector. They were designed that way because there wasn't any use of adjacent bands so nobody bothered putting money and effort into making them any better.
--scott