[anonytrary]

Pure simplicity works well when you have little to no users. It's reasonable to think that

  ORDER BY tweet.time DESC

would result in a impractical experience for a site that has millions of DAU.

[lvturner]

Only if you subscribe to everything - if you keep your follower list small, the individual experience doesn't change regardless of the overall size of the platform.

[Nextgrid]

Why would it be? It'll naturally keep your list of followings small (as a large one will be unmanageable) and promote quality over quantity.