I am not sure what I'm looking at here. Surely those half million files are for dozens if not hundreds of different apps, libraries and tools and surely those do not all depend on each other, no?

Because if so, why not just use one repo per app/library/tool? Sure, if you have a cluster of things that all depend on each other, or a cluster of things that typically is needed in bulk, by all means, put those in a single repo.

But putting literally all your code in a single repo is not a very sane technical choice, is it?