Another dimension to this is the need for sequence-breaking to be able to work.

For example, if someone does the Alexander quests first, and then catches up on Crystal Tower later, things still make sense with respect for our Garlond Ironworks people. Likewise, if we start seeing Allisae in the main scenario soon, it still needs to be possible for the Binding Coil quests to happen at any point in the relative past or future.
Some quests will get text amendments acknowledging progress flags (hello, Azure dragoon), but these can only examine relatives else things start breaking.

And no one wants their wibbly wobbly timey wimey stuff to start feeling jumbled.