Originally Posted by
Revolutionary_Jack
Because it's not the same thing. A villain in a superhero story is a dynamic audiovisual experience. Choosing the villain by itself designates the kind of action, setpieces, props, and so on you are gonna use in the story. The supporting cast by themselves don't bring a lot of visual elements. They are primarily there to maintain consistency, characterization, and provide the subplots that delivers the broader emotional experience of the project. So the supporting cast can stay the same but the villains have to change otherwise you are gonna get samey stuff. The worst example is Superman, where the only bad guys he ever fights are Luthor or Zod. Snyder then introduced Doomsday as a clone of Zod made by Luthor, because why not. As such all his movies tend to have same beats and moments. Luthor's gonna monologue with kryptonite, Superman fights Evil Kryptonians and stuff like that. There's no variety, no new visual elements and new action scenes that shows a different aspect of Superman and so on.
That's why stuff like not doing Jameson, Robbie, or addressing Uncle Ben, doesn't work. They are part of Spider-Man's story and provide the unique texture to his stories and are the reasons why a Spider-Man story doesn't look and feel like any other hero's. They also can't be replaced or overwritten.