Atheism is the belief that there is no "higher being". Atheism contradicts all forms of creationism and Lucifer is a figure in creationist religions. By definition, Atheists cannot worship Lucifer as they do not believe that he has ever existed and if he did he wouldn't have any "godly powers". Satanists, by my knowledge, believe that the biblical figure Lucifer Morningstar is a "good" being. They believe that he is the true God Almighty and should be worshiped the same. Satanists believe that they themselves can achieve divinity, much like how Christians believe that they can go to Heaven, but by honoring Lucifer instead of honoring God and his Angels. Thus, since Satanists see Lucifer as God, which is a creationist belief, Atheists cannot be Satanists and thus most people do not see Atheists as Satanists.