IMO it's not really a monorepo. There's a single codebase really. The author didn't meet the real monorepo pain points yet. The author didn't mention git operations slowing down, CI not handling the scale of the commit events from a single source and so on, instability of codebase due to many parallel changes, painful merges etc.

The difference between 150K LOC and Google's largest codebase in the world is huge and AFAIK google has a monorepo.

From my experience real monorepo requires a lot of tooling and maintenance.