Mikelavigne has explained a major reason why analogue tapes are not used in the digital remastering or reissue process. Also, you would not want to risk damaging these tapes rewinding and fast-forwarding on the various tape machines during a remix/remaster session.
Many original tapes were stored in less than optimal conditions (improper temp, humidity, dirty rooms) and may have creases or oxide peeling from the tape. In that case, the studio will have to try and have them restored before archiving them to digital.
It's the same deal with original film and videotape storage. The Library of Congress has a large department devoted to the restoration and archiving of all formats to digital.
Many original tapes were stored in less than optimal conditions (improper temp, humidity, dirty rooms) and may have creases or oxide peeling from the tape. In that case, the studio will have to try and have them restored before archiving them to digital.
It's the same deal with original film and videotape storage. The Library of Congress has a large department devoted to the restoration and archiving of all formats to digital.