a repo is a repo - you're describing what is nowadays known as a 'monorepo' and it's a perfectly reasonable and desirable even exactly for the reasons you mention, except the 'distributed' part makes it very inconvenient to handle on dev boxes if it grows a lot.

in a centralized VCS there are viable CICD options like 'check the compiler binaries in' or even 'check the whole builder OS image in' which git is simply not able to handle by design and needs extensions to work around deficiencies. git winning the mindshare battle made these a bit forgotten, but they were industry standard a couple decades ago.