The old Blu-ray was very blue, they corrected it somewhat. Plus, it was the safest option for the 50th, seeing as how it’s the most beloved film of the series.
The old blu-ray also shows some of the same contrast-boosting issues as the other five. I remember seeing a screenshot comparison of the shot where the Reliant and Enterprise first approach each other and the 2016 re-restoration is much more natural looking. The first six were released all at once back in '09, which probably means the same person/people were responsible for the final tweaks on all of them before the discs were pressed. There’s even a bit of dnr on that first WoK bd, it’s just nowhere near as bad as on the others thanks to the restoration.
Meyer mentioned overseeing (or at least signing off on) an hdr pass of the new 4k master. Maybe Paramount will finally do fresh scans of the other five once the wheels get moving on Khan’s UHD release. Who knows when that will be, though. With Meyer’s involvement with Discovery I was thinking it might be around the time it premieres (whenever that finally ends up being). Or maybe they’ll wait until the next movie, but that project’s status seems very up in the air after Beyond’s middling box office performance.