There's also a difference in goals. The point of a paper is to convince an expert that the claim is correct. With an article, you can just assume that the claim

There's also a difference in goals. The point of a paper is to convince an expert that the claim is correct. With an article, you can just assume that the claim is correct (or give it any level of credence you want), because the point is to inform more than convince. So the article can skip or sketch all the showing-your-work and steps and proofs and just present the conclusions.