Part of what propelled Digg to stardom was the desire for a central "town square" that didn't yet exist in the 2000's, Web-centric internet. (never mind that Usenet existed - it didn't have a lot of the conveniences of web forums and had gotten overrun with spam, so it just wasn't part of the discussion). There were a few larger, topic-centric sites like Slashdot, Something Awful, Fark, Newgrounds, etc. These older sites had various limits on user submissions and barriers to entry, in part because it was out of their scope to try to do more than that.

Digg hit on the combination of user-submitted content, simple voting interface, and secret algorithm that has defined most of Web 2.0 - but spam, moderation and power users were always an issue, and the best answer anyone seems to have had to it is "decentralize more", which Reddit did some of by splitting things out into topical feeds again, but unifying the login and access to all of them and letting users self-appoint as moderators - in essence, give power users their own fiefdoms to keep the peace. Twitter likewise absorbed some Digg users because it relied a lot on user self-moderation of their feed. Other platforms went down the path of having the algorithm do more of the moderation and becoming more TV-like, which is more profitable but volatile since that makes the platform blameworthy for everything that slips through.

So, what I feel has happened since is mostly intensification brought on by being for-profit and taking investment capital, unlike some of those older sites which are still around and kicking. It's hard to resist changing your business model towards profit maximization when you've taken a lot of investment. But then, the useful service that Reddit was providing when it launched is a commodity now, and with federated social media, the power dynamics are even more diffused.

But every time this happens, there are people who want to stay behind, and that's because power dynamics aren't uniformly agreed upon. Some people don't want it to be objectively challenging to hold power, they just want a game they can win.