I think it’s unrealistic to expect a non-franchise game to be a top seller. Every franchise has years of player base, nostalgia, marketing, lore, etc that lead to sales, not just the merits of the game. Additionally, most franchise games are data driven refinements on past recipes that work. Listen to feedback, make changes. And often times players buy franchise games with the expectation that it’s mostly the same but a little different, and in some cases that’s desirable.
It doesn’t mean franchises make the best games, it’s just unsurprising they’re top sellers.