Speed of development. It could take months for a PR to get into Lemmy core and then a new release.

Things that get into Lemmy core have to be well thought out and the core Devs have to want them in there.

Running custom code is a way to make changes without having to get their approval, and if it proves popular enough, then maybe they’ll implement it upstream.

So if you’re the only user (let’s assume for ease) then, that represents all the updates (posts, comments, votes) from each community that you are subscribed to?

That seems high when you extrapolate that to 10000 users, like a larger instance might have.