Character Development Doesn't Refer To Character Improvement In A Moral Or Ethical Respect. It Refers

Character development doesn't refer to character improvement in a moral or ethical respect. It refers to broadening the audience's understanding of that character, giving the character a deeper background, clearer motivations, a unique voice.

Developing a character is about making them seem more like a real person, and real people are flawed. Real people make mistakes. They repeat mistakes. They do things other people don't agree with. Real people are more than just 'good' or 'bad' and character development is about showing all of those other aspects of them.

Their interests and hobbies. The song that gets stuck in their head. The fact that their vacuum broke 3 months ago and they haven't gotten it fixed yet. All of those details help build out the character and develop them more.

And yes, characters change as stories progress but that doesn't mean they get 'better' in a strict moral sense. It means that their experiences change the way they interact in the world you've written for them. Just like real people do.