I think the challenge arises in ascertaining whether or not there is an adverse incentive driving their reporting on a given story. In the case of Snap it seem

I think the challenge arises in ascertaining whether or not there is an adverse incentive driving their reporting on a given story. In the case of Snap it seems safe to conclude that someone asked them to write positive stories. The need to disclose all potential conflicts arise because we cannot trust the authors of these sponsored stories to honestly disclose that that is what they are.