Digg fundamentally changed the way their site worked to highlight content from power users.
When you become huge, inertia is incredibly strong.
It's all about enthusiasts and early adopters (who are very fickle) and late adopters and laggards (who are very much the opposite of fickle). Crossing the chasm. Reddit has crossed the chasm.
Even though the rest of the world is literally flooded with US political news (less so now that Trump is gone), most of the rest of the world doesn't really care about those things Americans are super passionate about.
Reddit can remain huge even if half its US userbase leaves it.
This point is even more salient for Facebook outrage, BTW.
The only way a new platform can compete with them is by having the individual communities of reddit move to it with individual governance and then, allowing these communities to interact with each other in some way. The alternatives that look promising today are based on ActivityPub, but they fall into the same trap that reddit has: they want to appeal and attract as many users as possible without regard for suitability or community building. I'm hoping that the ting I'm working on will be better, but I'm not there just yet.