With the vagaries of IP ownership and deals and whatnot, I assume that the only income that mangaka can count on are takoban sales... so I assume having more volumes just makes more business sense in the long run. Like the person who wrote Sailor Moon, who hasn't really done anything since, but probably makes some kind of income from people checking out the manga.
I don't know much about the yaoi world, but a lot of the yuri manga people seem to work hand to mouth and churn stories to make up for not being able to have hundred chapter books. But a lot of them disappear and give up after a single volume... I think only Takemura Jin and Moringa Milk are the only ones who have had any longevity (based on the stuff available in English at least), and even they feel mostly like grinders who are supported by LGBT communities more than anything else.
Are there guys who just tell short shounen stories over and over again and grind out a living by publishing 6 chapter single tank stories in Shounen Jump? Because that sounds like an impossible way to make a living in Japan.
(Of course, in terms of other artists in my previous post, I totally forgot about Adachi - who survives by writing the same baseball manga over and over again.

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