Could you potentially explain what makes it "some of the most garbage software imaginable"?
edit: wording
I'll wait.
Honestly, I'd genuinely like to hear some of the answers to this, or even just mentions of good codebases to explore.
That said, I don't think that there will be that many that satisfy all of the requirements listed here, because as the scope of a project grows, there will almost inevitably be some technical debt or accidental complexity, or even subjective things.
That said, there are three things to consider: 1) I honestly don't care whether you think it's garbage or not. 2) I saw some amazing software there, and I saw some that wasn't amazing. 3) It's an immense business, and there is a certain amount of inherent dysfunction that comes with that many people working on anything together much as you would see at any large company.