Enough of the members of the Alliance had day/night cycles that all Alliance starships ran on a 10 on, 10 off system that didn't suit anyone but didn't ruin anyone either.
This would cause problems, as in space, most things didn't care about doing things on such a schedule.
So it evolved into less a day/night cycle and just two equal teams taking turns running the ship.
Unfortunately, as much as day/night cycles were ubiquitous enough to warrant their implementation, the only thing more ubiquitous was arbitrary divisions leading to competition, which inevitably led to attempted sabotage.