Side content in a large role-playing game tends toward a small number of shapes. The repetition follows from how optional content has to be produced rather than from a lack of ideas.
Optional content has a lower cost ceiling
Main story content is seen by nearly every player, so bespoke animation, voice acting and level construction are justified. Side content may be seen by a minority.
Production budgets therefore allocate far less per hour to optional material, and the difference has to come out of something visible.
What survives the reduction is structure and text. What is cut is unique space, unique animation and unique consequence, which are the elements that make content feel distinct.
Quests are assembled from a small set of verbs
The actions a game supports are fixed by its systems: travel, fight, talk, collect, escort, defend. A quest can only be built from these.
Content teams therefore work from templates that combine verbs in different orders, varying the location, the target and the framing rather than the underlying activity.
A player who completes a few quests experiences variety. A player who completes fifty is sampling the template set often enough to see it directly.
World space is reused because it is expensive
Building an environment is among the costliest work in a large game, and a location used once is poor value for the effort it took.
Side quests are consequently routed through areas the main story already established, which is efficient and makes the world feel coherent.
The cost is familiarity. Returning to the same locations for different reasons flattens the sense that each task is its own journey.
Progression systems require quantity
Levelling curves need a certain volume of activity to pace correctly, and side content is what supplies it. The design needs the hours to exist.
That requirement pushes toward content that can be produced in bulk, which is the same pressure that produces templates.
Games that reduce the volume typically flatten the curve as well, since fewer tasks cannot fill a progression built for many. The two decisions have to move together.
What makes side content memorable is expensive
The quests players remember usually have a consequence that persists, a location built for them, or a character whose situation changes. Each of those costs main-story money.
Studios that concentrate optional content into fewer, larger pieces produce more memorable results and less total content, which reads as a thin game to some players.
The trade is therefore between breadth and density, and it is decided by budget allocation long before any individual quest is written.