Sales decline for these series preceeds Corono and KnY boost.
Kimetsu doesn't stop you from buying other series and for series as big as HQ & MHA, it also doesn't push your new releases out of the charts completely.
Yes, yes it does.
I mean sure, it´s probably not a
HUGE drop because Kimetsu cannibalized other series' sales, but there´s only so much money that people have to spend on "hobbies", imagine for example there's this guy goes to Seven Eleven and only has a 1,000 yen bill, this guy buys some food, but he only has around 500 Yen left! sees the new Kimetsu and the new MHA volume.. He has to make a decision and decides to go for the new Kimetsu volume, "I will buy the new MHA volume other day.." And that day never comes..
That's probably happened sometimes, I mean I know it has happened to me, I intend to buy some series but I just kinda lose interest over time, it's impossible to buy every single series you want to for most people... Even if you did, I doubt you would have to time to actually read every series, unless you actually dedicate all your free time to it.
I mean if we put all the different factors that are maybe contributing to different sales together:
-Readers finding the series got boring or stale. (Which happens for most series after a couple of years, especially one-two years once they get their anime adaptation).
-Coronavirus (I'm pretty sure this must have lead to a decline in sales, no matter how low, even in Japan which supposedly is "fine").
-Kimetsu no Yaiba cannibalizing other manga sales.
If each factor takes 5% away from other series' sales that's a 15% decrease right there. If MHA used to sell I dunno 750,000 copies a 15% decrease is 110,000 less volumes sold.
What I think lots of people don't see is that Kimetsu hit the mainstream big time so
IT IS cannibalizing other manga sales, if a "normie" that used to buy say I dunno say 10 volumes of manga a month (Like a 5,000 Yen budget) and I don't think "normies" would buy that many volumes anyway but let's just use this hypothetical example, they'd probably buy the new Kimetsu over other manga they follow and maybe never buy that series again.