Curation. Art and design products meant that you could actually "shop" on the site (until risks forced them to require better disclosure), and interest in one type of project would lead to discovery of other similar projects. The homepage also allows for staff to pick projects that better represent the types of projects that might be successful. Indiegogo and Crowdtilt, among others, are more willing to accept anything.
https://www.kickstarter.com/blog/kickstarter-is-not-a-store