Now, at IEEE Spectrum, Marty Perlmutter's The Lost Picture Show: Hollywood Archivists Can’t Outpace Obsolescence is a great explanation of why tape's media longevity is irrelevant to long-term storage:
While LTO is not as long-lived as polyester film stock, which can last for a century or more in a cold, dry environment, it’s still pretty good.Note also that the required migration consumes a lot of bandwidth, meaning that in order to supply the bandwidth needed to ingest the incoming data you need a lot more drives. This reduces the tape/drive ratio, and thus decreases tape's apparent cost advantage. Not to mention that migrating data from tape to tape is far less automated and thus far more expensive than migrating between on-line media such as disk.
The problem with LTO is obsolescence. Since the beginning, the technology has been on a Moore’s Law–like march that has resulted in a doubling in tape storage densities every 18 to 24 months. As each new generation of LTO comes to market, an older generation of LTO becomes obsolete. LTO manufacturers guarantee at most two generations of backward compatibility. What that means for film archivists with perhaps tens of thousands of LTO tapes on hand is that every few years they must invest millions of dollars in the latest format of tapes and drives and then migrate all the data on their older tapes—or risk losing access to the information altogether.
That costly, self-perpetuating cycle of data migration is why Dino Everett, film archivist for the University of Southern California, calls LTO “archive heroin—the first taste doesn’t cost much, but once you start, you can’t stop. And the habit is expensive.” As a result, Everett adds, a great deal of film and TV content that was “born digital,” even work that is only a few years old, now faces rapid extinction and, in the worst case, oblivion.