I think the biggest issue is that people think since fantasy is all make believe it's easy and anyone can do it. That may be accurate to an extent. The fact that fantasy can be anything your mind can imagine is true but making that story something people want to read is different. To make a book something someone wants to read requires a lot of effort. We have to create a land, i.e. Middle Earth, Narnia or even Hogwarts. The story was about the characters, the land and how they interact together. It's just as hard as any other genre of book. The reason people write it I think is because it allows our imaginations to flow. A unicorn in Harry Potter makes sense, but one in a mystery novel doesn't unless it's fantasy based.