A single episode can contain a sequence of remarkable fluidity and, minutes later, a scene that looks noticeably cheaper. The variation is a direct consequence of how the work is divided among people.
An episode is split into cuts and handed out
Production divides an episode into individual cuts, each assigned to a key animator. Dozens of people may contribute to twenty minutes of finished film.
Those animators work at different levels of experience, on different schedules and often at different companies. Some are staff, many are freelance, and some are working across several shows at once.
The episode is then assembled from their returned work. Consistency depends on supervision rather than on a single hand, and supervision is the resource in shortest supply.
Effort is allocated deliberately, not evenly
Directors decide in advance which moments carry the episode. Those cuts go to the strongest available animators and receive the most drawings and the most correction time.
Everything else is produced to a standard that reads acceptably while consuming far less of both. A conversation in a static room can be carried by a small number of drawings.
This is a rational distribution of a fixed budget, and skilled direction makes the difference invisible by placing the plain material where attention is lowest.
Schedules compress unevenly
Episodes are produced in overlapping cycles, and delays in one push into the next. The pressure does not fall evenly across the episode.
Cuts returned late receive less correction, and sequences reworked at the end of a schedule cannot be given the passes they need.
What a viewer perceives as an inconsistent episode is frequently a chronological record of when each part was finished.
Outsourcing widens the range
Substantial portions of most series are produced by external studios, sometimes in other countries, working from supplied layouts and instructions.
Quality varies with the studio, the brief and how much time the supervisors had to correct returned work.
Where correction time runs out, the differences reach the screen unresolved, which is why variation often clusters within particular episodes rather than being spread evenly.
The strongest sequences depend on individuals
Distinctive action sequences are usually the work of one animator given unusual freedom over a whole passage, which is why they have a recognisable personal character.
Audiences increasingly identify these people by name, and the credits make the attribution possible for anyone who reads them.
That visibility has changed careers within the industry, though it has not changed the underlying structure that makes such sequences rare within any given episode. One animator can only be in one place, and every episode has to be finished on the same date.