It's not a matter of "can't be bothered." Engineers are constantly fixing things and rolling out new features. "Error budgets" are an acknowledgement of the tradeoff between these two things, and making a conscious choice about the balance between them, according to the business requirements of the application in question.

Keep in mind that "fixing things" is essentially a Sisyphean task - no matter how much you do there's always more you can do. Just like adding features. You have to have some kind of guideline on when enough is enough.