A series can be widely praised, widely watched and still end after one season with the story unfinished. The decision sits with a group of companies whose interests are not identical to the audience's.
A committee decides, not the studio
Most television anime is financed by a production committee, an arrangement in which several companies invest and share the rights.
A publisher, a music label, a broadcaster, a merchandise company and a distributor might all hold shares.
The animation studio is frequently a contractor paid to make the show rather than an owner of it.
A second season requires the committee to agree, and any member can decline to fund another round.
Because the members have different reasons for being there, they measure success differently.
The series is an advertisement for something else
For the publisher on the committee, the anime exists to sell the manga or novels it adapts.
If the adaptation produced a large increase in source sales, the publisher has already received what they came for.
A second season is only worth funding if it will produce a further lift, which depends on how much unadapted material remains.
Where the adaptation covered the most commercial portion of the source, the case for continuing weakens.
This is why a series can be a commercial success and still not be continued.
Disc sales stopped being the deciding number
For a long period, sales of physical releases were the clearest signal, and a threshold figure was treated as the mark of viability.
That market shrank substantially as streaming became the normal way to watch, and the signal degraded with it.
Streaming platforms have viewing data but do not generally share it in a form the whole committee can act on.
Merchandise, mobile game tie-ins and event attendance now carry more weight in the assessment.
The consequence is that the criteria are less visible to audiences than they used to be.
There has to be source material left
Adaptations frequently catch up with ongoing manga or novels, at which point there is nothing more to adapt.
Waiting is the standard solution, and waiting takes years because the source is produced at its own pace.
The alternative is original material written for the anime, which risks contradicting the source later and is unpopular with existing readers.
A gap of several years is itself a problem, because audiences disperse and cast availability changes.
Some series return after long absences precisely because the source finally accumulated enough chapters.
Studio capacity is booked years ahead
Even with funding agreed and material available, the animation has to be made by someone.
Studios commit their schedules far in advance, and the team that made the first season will have moved to other projects.
Reassembling that team is often impossible, which is why continuations sometimes change studio and look different.
A change of studio can alter character designs, colour and animation style noticeably.
Audiences read that change as a decline in care when it is usually a scheduling outcome.
The staff cannot be held together
Anime production relies heavily on freelance labour, and freelancers work continuously across productions.
A director who wants to make a second season may be committed elsewhere for the years it takes to arrange one.
Voice actors are easier to retain, but they too have schedules, and long gaps introduce risk.
The specific combination of people that produced a distinctive first season is rarely reproducible.
What returns is the property, staffed by whoever is available at the time.
Streaming money changed who sits at the table
International platforms now contribute directly to production, sometimes buying exclusive rights outright.
That has increased the amount of money available and increased the number of series being made.
It has not increased the number of animators, so the same labour pool is spread across more productions.
Platform-funded continuations are decided on platform metrics, which can favour series with sustained international viewing over domestic merchandise performance.
The result is a different set of series being continued than would have been a decade ago.
The ending of a first season tells you the plan
An adaptation that stops at a natural arc conclusion was probably designed as a self-contained twelve episodes.
One that ends mid-arc, or with a character introduced in the final minutes, was made in the hope of a continuation.
A final shot of an unexplained character is a standing invitation that the committee may never accept.
Announcements of a sequel at the end of a broadcast indicate the funding was agreed before the first season aired.
Silence after the credits is not a verdict yet, but it does mean nobody had committed by the time the episode was finished.