This. All of this. Like, granted, the OG creator was a hentai artist beforehand, so if you knew that, you knew what to expect. But even then -- with mangas and animes that don't have that background, they try to sell this serious story but all I'm getting is this forced fanservice with the mandatory beach episode.
Case in point: Infection by Oikawa Tooru. I was sold a story about vicious flesh-eating zombies that evolve and stuff. I was sold a story about high school students trying to survive this undead infection. What did I get?
A goddamn sexy harem that just takes place in a zombie Apocalypse setting.
Like, ok, fine -- it's something fresh and new. But that's not what I came for -- if you sold me the zombies, I should've gotten zombies. Now the zombies appear less in each chapter (to the point where I wouldn't KNOW it was a zombie invasion if I just read the newest chapter), and it's all about this harem. It happened within certain parts of The Walking Dead tv series, and that was why I stopped watching that. I don't care about the human dramas or the sexy times. You sold me zombies, I want the zombies.
I think a lot of times, the large amount of forced NSFW/fanservice is given to stories where the creators believe the plotlines are utter shit, so we're supposed to stick around because "hey look -- you saw some hot NSFW action!"