I think it does have to do with the topic, because it answers the headline question "why do fantasy novels have so much food"; I literally came to this comments section to remark that the answer is likely to do with the fact that engaging all of a reader's senses is a common literary trick to make the reader feel like they've been transported into a world. Turns out, eating food is one of the most common ways to engage the sense of taste. :P The author of the OP is probably being a bit narrow in that this isn't something confined to just fantasy, but if one were to somehow prove that this is a trope that's uniquely prevalent in fantasy (which the author doesn't), then the further answer would probably just be, like many other fantasy things, "because Tolkien did it". But really, when Rowling describes a Hogwarts feast it's not because she's trying to check off the I-wrote-a-fantasy-book checklist, it's because eating is a familiar sensation that helps the reader establish a firm relationship with a setting that is often otherwise deliberately alien and mysterious.
