With a monorepo, how do you avoid the situation where almost every time you want to commit, you have to pull-and-rebase first? Because somebody has always pushed a change, every minute or two.
In a repo that large, you don't want to have random people pushing to master anyway. Have people commit to branches, and then automation merges the approved branches into master. ("Automation" may be as simple as the "Merge" button in Github's UI, or more complex if necessary.)