It is like asking why do people like sonic characters (sexually) people liking アニメ characters, ディズニー characters etc. beyond your imagination. So your 質問 is not hard to figure out, または anything. It's just a simple answer; because they think she's hot. There that simple.
Here is why 1) People think she is just hot, but i would rather say she is beautiful 2) She is very powerful monster and she might have been very 人気 because she is the student of Dark Magician 3) she has a good ability 4) She is actually a good friend of Atem in ancient times