I never worked at Google, but this post sums up everything I had to say about the matter. GP has a sh-tty monorepo experience at one company and decides to make a statement about another company where they never worked (so I presume). HN absurdism as its best!

I second your point about monorepo versus ball of mud. They are so different. And managing all of this is about social/culture, less science-y. If you don't have good culture around maintenance, well then, yeah, duh, it will fall apart pretty quickly. It sounds like Google spends crazy money to develop tools to enforce the culture. Hats off.