Query about the syncing of subscribers numbers between instances.

This may have been answered before, but I cannot find a definitive answer to this.

This doesn't necessarily apply to Kbin/Lemmy as I have seen this before with Mastodon and never thought to ask

The number of people that are following https://kbin.social/m/fediverse is not the same as if it were viewed from Lemmy.world.

On Kbin, it's showing 8836 subscribers, but on Lemmy.world, it's merely 485 subscribers.

I understand that it is showing 485 lemmy.world-specific subscribers are subscribed, but my question is:

Why can't the numbers of subscribers be close to or not be the same as the actual number in other instances?

For this particular example, is it a Kbin/Lemmy thing? Is it an ActivityPub thing? Or is it a side-effect of how the Fediverse works?

My thinking was that the synchronising of numbers between instances may be either broken/disabled due to the server load or the feature on the software side of things has not been implemented.

Any help would be appreciated. :)