I’m saying this in the context of the root comment claim that there is anime for everyone. Only a very few anime series are mainstream in the same sense that Marvel movies are mainstream. Continuing that analogy, most anime series are more akin to serialized superhero comics, which are only read by relatively few. Looking at the shape of the distribution here is important.
I think the main issue they didn't do a distribution, they just asked a single question without a range from weekly to daily, etc. etc. Most folks were probably too shy to admit it as a regular thing, but also didn't have a sometimes option.
To me it's just bad data, pretty much asking for folks to be like "no". But also I can't find anyone having bothered to do any other data collection on it.
