Why do Atheists call God the Almighty magical and a sky fairy ?
God has nothing to do with magic. Magic is when a human uses evil spirits or other mysterious forces to achieve specific goals. God on the other hand is not human and has no hand in any magic that takes place. God doesn't live in the sky either. God probably transcends the whole universe. God is not a fairy. Because God is not female. God doesn't have magical powers. God has powers that are not comprehensible by us but they are not magical.
Because that's basically what it is. By magic, I mean anything supernatural. You believe God has magical powers that can reshape reality in any way despite that violating just about every law of physics. That's magic. You're defining 'magic' very narrowly. I'm not.
Sky is in there because he's in heaven, and heaven typically is associated with puffy clouds and what not.
And fairy, because fairies are a broad classification of magical beings. I didn't say God was female, and nothing about fairies implies femininity. Though, to be honest, the power of CREATION really is a more feminine trait than a masculine one. But fairies include a wide range of magical make believe creatures.
Sure, the description of "magical sky fairy" is uncharitable, and not ENTIRELY accurate...but it's not entirely INACCURATE either. I use the term at times to drive home the point that God is a childish make believe creature with no evidence for his existence...just like magic and just like fairies.