Google is an advocate of monorepo. However a lot of people are seem to be regurgitating what google wrote about them, but they are not Google scale and have no idea what the problems Google faces are.

Google also is very much in the yell loudly and ignore anyone who points out the problems of a monorepo.

Maybe it is just because I know a lot of Googlers/ex-Googlers, but almost all of the advocates for monorepos that I have spoken to are basing it from their experience at Google. I won't disagree that they tend to gloss over the extensive tooling they have to make it work, though...