Backup tapes contain a complete image of a business' production data. A used backup tape should never be casually thrown away. No industrial spy ever restored a backup tape that had been minced by a large axe. Media longevity is another point. Any backup tape rotation should include a provision for rotating out old tapes and replacing them with new ones.
Tapes simply wear out over time.
Brand new tapes need a break-in period. During the first couple of times of use, new tapes will lose tiny amounts of loose magnetic material. Intersperse all new tape insertions to the rotation stack with seasoned tapes. Drives need regular maintenance. Regular alignment and, especially, cleaning of tape drives is most important.