So we should all write bad code to keep it predictable? raising the quality of the codebase is unacceptable under this premise.

Possibly. Probably even.

High quality and consistent > Low quality and consistent > Variable quality and inconsistent. If you're going to be the cause of the regression into variable quality and inconsistent you'd better deliver on bringing it back up to high quality and consistent. That's a lot of work that most people aren't cut out for because it's usually not a technical change but a cultural change that's needed. How did a codebase get into the state of being below standards? How are you going to prevent that from happening again? You are unlikely to Pull Request your way out of that situation.

"So we should all write bad code to keep it predictable?"

its true and false at the same time, it depends

here I can bring example: you have maintaining production system that has been run for years

there is flaw in some parts of codebase that is probably ignored either because

1. bad implementation/hacky way

2. the system outgrow the implementation

so you try to "fix" it but suddenly other internal tools stops working, customer contact the support because it change the behaviour on their end, some CI randomly fails etc

software isn't exist in a vacuum, complex interaction sometimes prevent "good" code to exist because that just reality

I don't like it either but this is just what it is