Sean Malstrom's theory about the drought is that Nintendo went full steam on the User Generated Content idea, Wii Music failed (and so did Little Big Planet) and showed them that UGC is a terrible idea so they had to freeze a lot of projects for retooling to outfit them with proper content instead of UGC and that's why they had nothing to release, they wanted to release something but messed up. That probably didn't delay S&P2 but I wouldn't be surprised if e.g. Minis March Again was originally intended to contain less premade content and instead rely on UGC.