That is one of the many reasons why torrents that consist of a collection are a problem.
To solve this problem, downloaders stop seeding, which causes there to be fewer seeders for the torrent.
There are many torrents of large collections that are dead. If the videos had been in individual torrents, it is likely that at least some of them would still be alive.
The more videos in the collection and the less well-defined the theme, the more likely it is that someone will only partially download the torrent.