Linux also has the huge advantage of an ecosystem, tools and integrations. It is overkill for small projects and there are friendlier alternatives for those - but git wins because it is what everyone knows. Something aimed at the small number of large projects will suffer the same problem.
In terms of number of commits, Linux is probably bigger than most. In terms of storage size, almost any video game project will be significantly bigger.
It's no secret that git is very bad at handling large binary files.
No, large companies using monorepos will have repos much bigger than Linux even without large binary assets. Apparently Linux has ~10 commits per hour. I probably do ~10 commits per week. So a team of ~150 mes produces commits at a fast rate than Linux. Very rough estimate but it takes less than you'd think.
Also if you vendor a few dependencies that quickly increases the size.
Linux also has the huge advantage of an ecosystem, tools and integrations. It is overkill for small projects and there are friendlier alternatives for those - but git wins because it is what everyone knows. Something aimed at the small number of large projects will suffer the same problem.