LN manga adaption seems to get axed a lot. Feels bad man
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A lot of author do this on purpose sometimes. We called it "Promo series" where they end half way and tries and get ppls to buy into their source material.
Tho some does get "axed" because it wasn't that high in the "rankings" in manga. Sometimes it has nothing to do with sales, sometimes it does.
If a series have moderate sales but low ranking, it gets axed.
But if a series have moderate sales, but high ranking, it continues. And vise-versa.
Such as series like To-Love-Ru and other ecchi romantic comedy series that have high sales but low ranking cause ppls don't want others to know they're pervs, the series continues regardless of ranking.
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In any case, most of the time series that gets Axed are typically "unique" series.
Meaning series that's not with the "trend" (IE: the BIG series with 100+ chapters and/or cliche action adventure shounen series that focuses on Ecchi/ Violence)
There's a reason why high ranking series all tend to have similar plots...
It's pretty much the same as "Gaming trends"
Such as how gaming moved from MMORPG to FPS to Survival to MOBA to Hero Shooter to Battle Royal. It's why MMORPG are kinda dead now, no company makes them anymore besides Korea... and every company now makes or add Battle Royal into their games.