In a way it strikes me as odd that what a substantial portion of the population relaxes with is stories of violence and mayhem and suffering: except in my case it's sanitized violence and mayhem. Not quite cozy Agatha Christies, but at any rate relatively civilized British murders with relatively civilized Inspectors doing their jobs. All well and good: but when asked what I did with the last five years of my life, will I have to say 'I read a lot of cozy mysteries'?
I think it's because after a certain point nothing is mind-blowing. One looks for difference, for amazing things: and gets, in literature, the real or imagined problems of ordinary and generally unlikable people; in fantasy, tired tropes and dystopias; and so, well- one returns to comfort reading.