In response to your edit: Eleanor and Bojack both had rough upbringings that made how they turned out somewhat inevitable, but Bojack gained fame and fortune while Eleanor always struggled. Bojack had the resources and opportunity to turn his life around and be a good person, but he never did. He learned and grew to a degree, but relapsed more often than not and never fully grasped the impact he had on others. Too wrapped up in himself.
Eleanor, meanwhile, very quickly (and repeatedly) rose to the occasion when actually given the environment and opportunity to change. She showed real growth and rarely if ever slipped back into her old tendencies. She also showed genuine remorse for her past behavior after a while, while Bojack, by contrast, only seemed to feel remorse in a performative way to placate others or in a woe-is-me way when he actually faced consequences for his actions.
They may have started at the same place, but how they ended shows which of them was actually a good person.
In her case, it’s more that she was raised by trash to be trash.