"Great movies get lost or ignored for the same alchemy of factors that make lackluster ones into hits: studio politics, a given star's popularity (or infamy), and the current zeitgeist's appetites. Sometimes they're overshadowed by a gargantuan hit, as people forget other great flicks were released during the box office runs of The Godfather, ET or Titanic. They might have been legitimate successes upon release, but were forgotten with time.
Another strange alchemy is at play when they get rediscovered. Maybe recent events make them relevant, or they proved prescient, or critics look back at a decade and realize that picture never left them. Sometimes they scratch an itch Hollywood is ignoring or sometimes a hot director champions it as an influence. Somehow, someway, they end up speaking to audiences again. One hopes for some gorgeous Criterion restoration, and dreads the remakes, precisely because that alchemy is almost always impossible produce."