Reddit has been going through drama after banning one of its largest hate subreddits and sacking a public facing employee. This has spurred a large number of users to look for other sites.
A big factor in Digg's demise was that Reddit was a smaller, scalable competitor that was able to accommodate the influx of users.
This time Voat is there but it still isn't a viable alternative; given that it isn't able to scale its technology. If they focus on fixing this, then it's just a matter of time before everyone an incident occurs that decides the grass is greener over there.
I'm surprised that community happiness isn't taken more seriously at Reddit. It's their biggest asset, and the whole Digg experience shows that it can be lost so easily.