I used to have a flatmate who pretty much refused to read any fiction less than a hundred years old. When I stumbled across some writing on the development of more mainstream or literary fiction, I started to see his point. In the twentieth century, a lot of writers began to consciously move away from what they thought was too much of an emphasis on plot, and starting writing stories that focused mostly on character, with little plot development. Because a genre is mostly defined by specific plot beats (fantasy and Sci-Fi are more defined by their settings in my opinion, but let's skip over that for now.) This had less of an effect on genre fiction than on mainstream or 'literary' fiction.
Here's the problem. It's really hard to write a book with not much plot and actually have it work, and in my opinion, most writers can't pull it off. I've read many fantasy novels of varying quality, and never have any of them been about someone sitting in a room whining to themselves for three hundred pages. A lot of mainstream fiction these days is character studies with boring characters, so I hardly ever read it, but I can read these plot heavy nineteenth century novels no problem, even if the characters are pretty flat. Mythology has some of the oldest and most enduring stories in all of history, and the characters are often two dimensional archetypes.
I'm plot trying to say plot is more important than character, in many ways I think that's a false and unhelpful dichotomy. But for me, fantasy offers more than just imaginative monsters and magic systems I can't find elsewhere. It has epic, sweeping, important feeling stories that most mainstream fiction hasn't had for almost a century.
