Why do many visual novels contain erotic content? After watching/reading anime and manga, I recently started going into visual novels. One thing that struck me was the fact that erotic content (aka H-scenes) seems to be quite common in the world of visual novels. Examples: Fate/stay night, Muv-Luv Alternative, G-senjou no Maou. Can anyone explain this higher prevalence of erotic content in visual novels, as compared to anime and manga?
Because visual novels are spinoff of eroge games. According to wikipedia: 

The eroge game (or H-game, hentai game) are introduced into the market (no pun intended) in the 1980's as a means to attract users to the (game maker) company computer platform.

In 1992 the dating sim / love simulators were born, when a company designed the game so the player had to win the affection of the character before gaining access to the H-scenes.

The first use of the term visual novel is in 1996, and from there the erotic material became optional, with the introduction of the all ages versions of the visual novels.

But still adhering to tradition, the visual novels of today still have the H content, though not every one.



Refer to the wikipedia article to more in-depth historical facts, including game titles and company names.