Apple's rules for its developers are a bit conservative. While Android may have free reign over all kinds of offensive apps, Apple doesn’t want video games to be controversial or sexy.
From Apple's guidelines, according to VentureBeat:
We view apps different than books or songs, which we do not curate. If you want to criticize a religion, write a book. If you want to describe sex, write a book or a song, or create a medical app. It can get complicated, but we have decided to not allow certain kinds of content in the App Store.
U.S. & World
Essentially, Apple is saying if you want to be controversial or political then you should develop that content until it's a book. Games are not the place for politics, religion or sex. It's also one of the reasons it rejected "Endgame: Syria" a game that violated the guidelines because it targeted "a specific race, culture, a real government or corporation, or any other real entity." Because the game took place in Syria and based on the current civil war, Apple found it was too much of a political hot potato.
“I feel that the form of media should be irrelevant, and it’s the content that counts,” Endgame: Syria lead designer Tomas Rawlings told VentureBeat. “Games, films, apps, comics, music, and books should all be held to the same standard. To suggest that there is an invisible line that says it’s OK to say something in a book but not in a game? That feels wrong to me.”
Part of the problem is that games are viewed as frivolous, shallow entertainment, while books and pieces of art can be imbued with politics and controversy. Until games start tackling some serious issues on a regular basis, developers may find that their games will be considered trivial and be rejected from Apple unless they stay inoffensive and cliched.