Players routinely report that the memorable moments of a long role-playing game happened off the main road. That pattern is consistent enough to have a structural explanation.
The critical path carries every obligation
The main story has to introduce the world, teach the systems, service the marketing beats, gate the difficulty curve and reach a conclusion that resolves the premise.
Each of those requirements takes space, and space in the main quest is contested by several departments at once rather than allocated to whoever has the best idea.
What survives that process tends to be functional rather than surprising, because a scene that carries three jobs cannot afford to be strange.
Optional content can assume the player is ready
A side quest reached after twenty hours can assume the player understands the combat, the map and the factions, so it need not spend its opening explaining anything.
It can also assume commitment. A player who chose to go there is already interested, which permits slower pacing and a stranger tone than a mandatory scene could risk.
That freedom is where distinctive writing lives, because the quest only has to be good rather than good and instructive at the same time.
Optionality permits real consequence
The main story must remain completable regardless of choices, which limits how much any decision can genuinely alter, since every branch has to reconverge for later content to function.
A self-contained side quest has no such obligation. It can end badly, leave a settlement worse off, or close permanently with no route back.
Those endings feel weightier precisely because nothing downstream depends on them, so the writers are free to make the outcome unpleasant.
Smaller scenes are cheaper to iterate on
Reworking a main story beat can mean rerecording performances, rebuilding a level and rescheduling several teams, so late changes are resisted even when the writing needs them.
A side quest usually involves fewer assets and fewer dependencies, so a designer can rewrite it after seeing it played without disrupting anyone else's schedule.
More iterations produce better results, and side content simply receives more of them relative to its size.
Ownership changes the writing
Main quest scripts are usually written by committee, with the narrative lead, creative director and often the publisher reviewing every important moment.
Side content is frequently assigned to an individual writer who takes it from concept to completion, which produces a clearer voice even when the craft is comparable.
The trade is consistency. Distinctive optional quests sit alongside filler that received no attention at all, which is why side content quality varies so widely within one game.