For me, its Robert E Howard's
Sword & Sorcery fiction and Edgar Rice Burroughs'
Planetary Romance for the same reasons that makes
Twilight so popular: an escapist fantasy with a flat and overly idealized leading character that the reader can become immersed in, who has multiple love-interests, would become some sort of savior in the end, and lot of unlikely events with narratives that appeals to the reader even if its too idealistic. As dumb as that might sound, its actually a good thing. Its an outlet for our own dreams, desires and wish-fulfillment, that shapes our actions and creations to better things! Yeah Bella Swan is a terrible role-model, but her sense of romance is just as out there as an Earth-man who never acclimates to Marian gravity and outfights people who spent centuries of their lives honing their dueling skills, or a muscle-headed barbarian who is an academic savant and future king of a pridefully civilized nation. The details don't matter: they are all stuff a particular demographic really enjoys reading.
I have been working on a setting that is based on the old
Masters of the Universe mini-comics (the one that came with the figures; before
Filmation butchered the fiction and turned it into a damn Pride Parade!). Like early MotU, it is basically a universe-spanning war that left worlds in a barbaric stat, were people use magic alongside technology, and has lots of beefcake and cheesecake warriors. The chief technology that makes it possible for people to fight with swords along with blasters are miniature force field generators mounted on battle harnesses. They work like Holtzmen Shields from Frank Herbert's
Dune, in that they block range attacks (but would not nuke if you hit them with a laser) while allowing for slow-moving melee attack to slip through, because if you make the shield tighter, the wearer cannot breath. The tightness of the shields also trap body heat, so the wearer have to dress down for better ventilation, so no heavy armors. In other words, loincloths & leather straps and chainmail bikinis are now practical wargear!
WOOHOO!!! 
In my setting, worlds are connected by giant gates and people can travel by Barsoomian-styled airships. Each world is radically different, with their own ecology, cultures and dangers. The focuses of the setting are action, adventure, exploration, aerial-navel warfare, tribal politics, paranormal strangeness, and sensuality. Additional inspiration comes from '20s-'30s era pulps, '30s-'40s era movie serials, '80s cartoons, and cheesy '80s Sword & Sorcery movies. Its not meant to be taken too seriously, as its about trying to be as fun and awesome as possible.