Incredibly dumb question: What is the point of characters in a story?

I mean it seems super obvious but as I create more characters for my story, I want to absolutely make sure I understand why multiple characters are important.

The main thing I gleam is that characters make a story more interesting and give it more "depth". As I've been analyzing stories, I'm realizing that while the PLOT may stay the same when you remove characters, the story becomes less interesting, even if the plot and theme are intact.

Characters can also enhance the theme and characterization of the protagonist by providing contrast, as far as I can tell.

I don't know if I'm just over-complicating things, but I want to make sure I'm not adding useless characters, or the opposite, giving every role/important moment to one character when there should be another. Thoughts? :>