Maybe it is like those restaurants with dirty bathrooms. Most customers don't care, and if you get some minimum customers management thinks a bathroom makeover won't matter.
You're making it sound like having someone quit is a blocker. Some managers see that as shedding the dead weight, and keeping in the guys who are the team players with endurance. The guy who complains about code quality suddenly leaves and all of a sudden there are no more complains about code quality, and worst case scenario you have new joiners trying to onboard and cause a good impression who don't care if code is shit because their goal is to shine.
How did you solved that problem?
If it's one of the few business that has an absolute monopoly over a certain sector in a country, then the country will gradually weaken over time, until eventually it won't be able to resist a foreign competitor.
Or at least that's what market theory suggests. Of course the period of 'self-correction' could take a few months to a few centuries to fully play out, and simultaneously overlaps with all other market participants.