Why is there so much bad code at big companies?

Here is the excellent Sean Goedecke on why there is so much bad code at big companies. He's correct that: Many big-company engineers are working on relatively unfamiliar codebases, and this makes it harder to ship good code; Big companies prioritize things (e.g., legibility) that are not code quality; Code quality is partly a function of the code-review process, but code review is incentivized unevenly at best. (Those are all my paraphrases.) Those are all correct, but I don't think they're the most important drags on code quality at big companies. I'd cite these: Encapsulation is the main determinant of code quality; most engineers have not mastered encapsulation; and even 95th-percentile engineers struggle to get encapsulation right. Encapsulation is much harder at big companies, because systems have to be more complex at their scale. Simple solutions either don't work at all or carry costs that are negligible at modest scale but huge at big-company scale. (Authentication, load…