Digg and the mass exodus happened a long time ago so I could be wrong at parts. The very simple story is that Digg stopped allowing most people to submit links or something like that. I think they wanted to curate their own links instead of user submitted content.

Since Digg took away what made it popular, most people migrated to Reddit which at the time was more tech/developer focused.

Reddit filled the gap quite well and was more proactive about freedom of expression and knowledge. That slowly faded as time went on and it’s userbase grew. Throw in a few controversies and we have the Reddit of today.

That’s one of the reasons why leaving for Lemmy was so easy. I have seen it happen before. I’m already one foot out the door with Lemmy. PieFed has been making amazing progress and I know there’s interest and progress in making a migration tool for Lemmy communities/instances to switch over.