The Missing Footage
Time and Nitrate
Greed's missing hours are still missing, but the enemies of Hollywood's silent film archive --- time, neglect, nitrate and efficiency --- are against restoration.
Silent movies were shot on nitrate film stock. Nitrate films deteriorate over time and turn to powder and in between time, they are flammable. The studios made periodic inspections of their film vaults and tossed away deteriorating reels of film. Usually if one reel of a film was bad the entire print along with the negative and the finegrain were also tossed out.
For each film the studios usually kept an original negative, a master print and a viewing print, but did nothing to save what they had.
Typically, in the silent era a studio made about 40 prints of a film, and those original prints would stay in circulation for up to two years. When the print came back to the studio, it was usually beyond salvaging and thrown away. But the Greed's missing hours were never officially released.
Accounting and Efficiency
Studios, then as now, have policies to throw out unused footage after a certain number of years. When Steven Spielberg wanted to re-release a laser disc of Jaws with extra footage, he found out the footage had been tossed.
Generally unreleased footage didn't survive unless it got past the studio gates, or as in the case of the musical 1776, the editor intentionally mislabeled the film can so that the outtakes would be preserved.
The huge stacks of Greed's unreleased footage could have been a silent victim tossed in trash.
From time to time, the studios also unloaded reels of old films from their vaults to make room for new production. The old films were simply junked.
MGM held onto more films than other companies, but Universal dumped its stash of silents in 1948 to free up storage space for its new films, and all of Samuel Goldwyn production's were destroyed to save money on insurance premiums.
As Norma Desmond pointed out in Sunset Boulevard , "So they took all the idols and smashed them --- the Gilberts, the Fairbanks, the Valentinos. They trampled on what was divine. They threw away the gold of silence."
The dumping and neglect of the silents began as soon as theaters were wired for the talkies. There was little or no interest in silent films by the public or their producers, and soon there was nowhere to show them. And if a film could survive the hand of man, it still had to survive the hand of fate, of fire.
Disasters
Fire claimed a good portion of the silent survivors. The '37 Fox Little Ferry fire in New Jersey burnt up Fox's inventory of negatives and masters, and in 1970 MGM's film vault caught fire. Smaller conflagrations were frequent and common, and then even Unsinged footage would be damaged by smoke and water and then junked.