My assumption on why Kickstarter is so restrictive is because they are trying to create an atmosphere of trust between the Backers and the Creators. They are probably choosing projects that are more likely to be funded and finish a product, so that people feel safer pledging their money. On the other hand, Indiegogo is trying to compete with Kickstarter, and has less restrictions in order to get projects that Kickstarter won't accept. This is my assumption, so I may be wrong.