Check out this great article by Kit Sun Cheah, readers:
People enjoy the exotic, but not too exotic.
People enjoy the familiar, but not too familiar.
Reconciling these twin desires is the overriding concern of the modern-day fiction writer. A story where everything is formulaic, from characters to plots to setting, is predictable and boring. A story where everything is exotic and unfamiliar is disorienting, turning off most genre readers.
This is the strategy of writing to market. Understanding what readers want, carefully incorporating all the right genre tropes in your story, putting your own spin on the tropes while keeping strictly to genre conventions, and pushing it out to a highly targeted audience. An excellent strategy, one that works for many writers in the business.
LitRPG is the perfect example of this. Sword Art Online is arguably the most famous progenitor of the genre. The story fuses game-like mechanics, a fantasy setting and a self-insert protagonist surrounded by beautiful women. This formula appeals to hardcore gamers familiar with fantasy role-playing games, and with audiences who enjoy fantasy stories. The audience rewarded the writer with fame and commercial success, spawning the LitRPG genre. Today you see LitRPG variations of all kinds, from death games to VR MMORPGs to RPG mechanics in the real world.
Today, with Amazon opening the floodgates to self-publishing, this effect is even more pronounced. Book sales are driven by whales, readers who obsessively read books within a single genre—but only that genre. To reach commercial success, you must hook these whales, who will then recommend your books to their social circles, who are composed of fellow whales, who will in turn recommend your books to other fans. Write for them and the money comes in.