@atomicpoet
No one knows what exactly the algorithm does on twitter, but it has to have significant random factor.

I would guess that when people sign up, they get a sort of digital "lottery draw" in the background which semi permanently sets their visibility. Dynamic factors may later alter that, but barring that, some hit the jackpot and others don't.

How else are you going manage the visibility of 100's of millions... may as well be randomly set from sign-up onwards.