Part of the reason why I think it could've been just as successful in the main magazine is because it hits all the spots that current readers are looking for. It helps that it also went viral on Tumblr when it came out. Said Tumblr post also lists all the things readers were looking for, which would've also leaked into the Japanese readers.
The
"Fake Marriage" plot is a popular trope amongst fanfic writers, before Endo went ahead and used it in his original work. This is where Endo's genius comes in. Shihei Lin mentioned that Endo is the calculating type, and that's where the source of Endo's success comes from, by accurately analyzing a trend in fandom and using it to create his work.
PLUS SMOL ANYA.
I wonder about that too... you think going biweekly is a blessing for his health? If that's the case, we don't really know since we don't know the man well enough if he's physically up to the challenge of a weekly schedule.