I have absolutely no numbers to back the mobile assumptions I've made but with the rise of titles like Kancolle, which has had a meteoric rise in popularity because of all the cute girls getting fanart, fan music, fan everything, and even an anime adaptation after the fact - and the 'whales' involved being devoted to each 'girl' enough to spend lots of money ingame explain a lot.
The anime industry currently works like this: a lot of the money made back from the show is done by selling bluray sets to hardcore fans for 500 dollars or more. The devoted fans are the people spending the most by far on a show, to the point of buying everything from figurines to blurays to poster etc etc etc, sometimes even on a single character from the show.
I have a pretty solid feeling that this mentality makes mobile F2P games in Japan a perfect vehicle for getting more money out of these people.
Everyone seems to be getting on this bandwagon - the really popular Fate franchise is getting a mobile title, Fate/Grand Order - and it's no coincidence, I think, that a lot of the promotional material is centered around the cute girls that they want you to spend money on. Of course, I don't know how that title's revenue is made, but you get the idea.