In a blog post, Liz Upton explained that this was in part because the team put the Pi on the cover of their previous magazine the day the Pi launched, as well as their commitment to giving away profts and releasing their content under the CC-BY-SA licence.
"We’re very excited about this project. We know the team, and they’ve got some great writers and editors on board with a huge breadth and depth of domain knowledge and experience. These are the people who first put an article about Raspberry Pi on newsstands." wrote Liz."