In the current world where most of the forum discussion happen on Reddit, there is little space left for another active centralized forum.
The decentralized approach has at least the pro to offer something different (you can leave for another instance instead of depending on a single corporation for access).
Creating another centralize Reddit brings exactly the same issues current Reddit has (enshittification), and you don't even have the userbase to make up for it. Digg 2.0 launch was messed up, but even if they managed better it would be very difficult for them to get enough traction to really compete.
Bluesky is better that Twitter in a lot of aspect, but it stills fails to replace it, and the network effect keep bringing people back to Twitter to see "what is happening".
Vicinus replied in the other comment for numbers.