If you just scan at 1080p/2K, there’s a nonzero chance the pixels printed to the film won’t line up with the pixels being scanned, so you’ll lose information. 4K guarantees you’ll pick up every digital pixel that’s on the print.
In addition to preserving the look and texture of a film print, there are some changes made from this Film Theatrical Cut to the Digital Theatrical/ DVD release.
Per Wookiepedia:
"Most of these changes did not appear in the main theatrical release, but made it into a version shown in select digital theaters.
Several speeders were removed from a shot during the Bounty Hunter pursuit scene.
New dialogue added to the scene where Anakin confesses to the Tusken slaughter to Padmé.
Additional sparks and smoke have been added to Jango Fett’s jetpack shortly before his death to better present its malfunction.
After falling out of the gunship on Geonosis, a clone trooper asks if Padmé is all right. Her response of “yes” has been changed to a more realistic groggy “Uh-huh.”
During their duel on Kamino a shot of Jango Fett headbutting Obi-Wan is removed from the UK version of the film and DVD.
Anakin’s mechanical hand now holds Padmé’s hand during the closing wedding sequence (this was originally included in the DLP theater release of the film)."