Reddit demolished Digg because Digg actively antagonized it's most active users, and the will of the community similar to what X is doing.

Reddit had subreddits long before the migration. Reddit was a not very used site that had all the features.

It was Digg that made the decisions to force people off of it, not anything reddit did outside of having a space available that worked.

Digg just wasn't big enough. Once these networks get to a certain size they're unkillable. Look at all the turmoil reddit went through, a hated redesign, killed 3rd party apps, a whole protest movement, none of it mattered. People bring up digg and friendster but that was 20 years ago when these networks were way smaller. No top 10 social network has died since then.

Reddit had a much better system for commentary, as opposed to just reacting to URLs.

Sure, you could comment on Digg, but it was a pain and not good for conversations, and that meant there was less to keep people around when it seemed like the company was started to put their finger on the scales for URL-submissions.

I believe the big Digg-to-reddit migration happened before you could create your own subreddit.