Fediverse

The primary benefit to federated services as I see it is that you can have a network of groups, all with their own policies on moderation and who they federate with. Some corners of the Fediverse block other corners of the Fediverse, but each corner has their own policies on what they block. It's more democratized that way, and if you disagree with one instance's moderation policies you can move to another while still interacting with the same communities. Alternatively, maybe you prefer a different interface or way of managing your online presence! There's any number of reasons you would want to use a federated service.

It makes sense that someone who runs their own centralized service wouldn't see the need for a federated service, because they can run their centralized service the way they want and don't have to worry about whether the staff of their chosen service agree with them, because as operator they hold sway over that.

One of the other benefits of an open protocol like ActivityPub is that people can hook into it in the future. For example, Pixelfed may be the only software solution in its class at the moment, but if someone wanted they could make their own independent version and it could be interoperable if they used ActivityPub plus the same conventions that Pixelfed does. Sure a platform could always create their own open protocol, but better to use an established open protocol instead of reinventing the wheel for every new service. That's even setting aside the possibility the some service will come along to unite all of the Fediverse under one app (Kbin is trying something like this I think).

Also they're totally wrong about the Kbin situation. Kbin is 100% compatible with Lemmy, if a little glitchy at times (early days, after all). It's only the main instance that's not federating, and that's because they are using Cloudflare to deal with the surge in popularity from Reddit. Under normal circumstances even the main instance can federate.