First, she's significantly more reserved than Diana was and doesn't court the media. She simply has a quite different personality.
Second, Diana came along when there hadn't been a pretty young princess to cover for a very long time, and at a moment in media history when royals coverage was changing a great deal, becoming more intrusive and less distant and respectful. The media went overboard in their coverage of her and, in a way, exhausted the topic -- and not just because she ended up dying. Young princesses are just no longer quite the "news" Diana was in 1981.
Third, there haven't been any scandals surrounding her. She's a young matron and mother, very focused on her family, and neither she nor her husband has been known to stray. All that is rather boring to the tabloid media.