It is likely that PewDiePie has a negative enough image that YouTube believes that associating a given brand with his content will not generate ROI for the advertisers. By demonetizing these videos 1) the advertisers win because their ads are shown more frequently in "profitable" spots, 2) YouTube wins because they build trust with their advertisers, and 3) YouTube wins again because they don't have to pay out to the content creator for valueless ad spots.