[peakaboo]

You listed the reason it's a mess yourself - many people worked on it and it's old.

For big companies there is no incentive at all for a developer to personally care about and do battle over things like code quality and reduce complexity.

If they are use any kind of agile (lol) system, it will just be about polishing the turd so it doesn't break and add features in some way that doesn't require big rewrites.