I think your missing the point I didn't say that they couldn't keep running if they have the ability to and I wasn't discounting that it helps Jump if they do. A lot of fans for a series tend to only read that one series, there are some that read more, but how many casual fans would you say actually try something new after that one series they enjoyed ended?
assume everyone who reads the magazine buy the manga (again
assume) and there are around 1.8 million circulation/week nowaday?
We have:
~ 10,000 people try something new (Love Rush),
~ 10,000 people try something new (Red Sprite)
~70,000 people try something new (Kimetsu), with a fair amount bother to vote in the reader survey..
~150,000 people (1/18) try something new (Yuragi), with a fair amount bother to vote in the reader survey.
~100,000 people (1/18) try something new (TPN), with a fair amount bother to vote in the reader survey.
again, assume old fans only buy 1 series each, you have about ~1/5 people trying out new series.
And that is not accounted for one people buying multiple series.
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"try something new after that one series they enjoyed ended?"
They grow out of manga.