Well, technically what I write should be called “speculative fiction”, as fantasy is usually about magic and monsters. But I think the word “fantasy” does a better job of capturing the feeling of what I do, and the traditional fantasy fixation with worldbuilding is something I truly feel mine. Also, it may be just me, but “speculative fiction” kinda feels like the literary equivalent of “significant other”: technically correct, but dry as hell.
Anyway, I could give you a dozen answers to the title question. I won’t, because a) I’m lazy as hell, and b) because my answer was already kindly provided by someone else. I’m talking about R.A. Salvatore, who in the preface to the Guide to Writing Fantasy and Science Fiction wrote:
The trappings of a fantasy setting allow me to walk the hero’s journey, physically and spiritually, to examine the role of a god or gods without tapping the prejudices of real religions, to crystallize the responsibilities to self and community in the face of fantastical danger, and to play with themes of our own world, like racism and sexism, in a safe enough environment to allow both the reader and this writer to let down our natural defensiveness regarding our own foibles and look at the issues honestly.
This, more than anything, is the reason I chose to write fantasy. Note that none of what Salvatore says makes fantasy an easy genre to write; on the contrary. Writing a good story without the ability to “lean” on the real world can be as challenging as doing the research necessary to write historical fiction. The theme of a fantasy story might be universal, but the content is not, and the risk of producing something that’s unoriginal or naive is very high. But, hey, nobody ever said that writing is easy, right? Right.