Most of the market is filled with these types of dating sims, because the original consumer base in the early 1990s was primarily made up of young women aged 20-30.
There are two stats (at the moment) in the game: Friendship and Love.
You don’t just spend your time on girls, you must keep training too (Knowledge, Charm and Strength).
Not only that, but there are more endings you can choose from, and many choices.
Most of these games use a tasteful fade-to-black for sex scenes, but some are sexually explicit or outright pornographic.
Called eroge (a portmanteau of "erotic" and "game"), these porn games are usually geared toward men, although there are exceptions.