The key factor in Digg’s demise was a flawed design that was too easily abused by users. Digg had no controls over user verification, so individuals could game the system by creating multiple accounts to artificially inflate the number of votes for their own content. Because Digg displayed content in order of popularity, most visitors saw and voted only on content that was already popular. This system created a vicious cycle in which a small number of dedicated users could push their own content to the front page and thereby gain more followers, allowing them to more easily repeat the process. As Digg grew, so too did its problems related to power-hungry users cheating and gaining undue influence over content.

Sounds like the same problem that every centralized social media ecosystem suffers from. The big difference between Digg and Reddit was that Reddit successfully monetized the “push me to the front of the queue” algorithm rather than engineering around it.