> CSV/SVN used to do that out of the box but everyone hate them now.

It's "CVS" and it lacks a concept for a repository-wide version (except, maybe, a timestamp). A repository-wide version is –I guess– the single best reason to have monorepo in the first place.

SVN is okay.

Also, `git log -- subdir/`.

Why aren't submodules more wide spread?

Building a monorepo out of submodules should solve these problems, or not?

Also, there is subtree.

Because submodules is hard to understand. They require that you understand git and that you can add one level of abstraktion.

Once you done that, they är great!

Also hard to deal with. Lots of operations leave submodules in unclean / out-of-date states.

In general / light use, yeah, they're great. Unfortunately, they have a very large number of edge cases where they essentially require either a) everyone to be experts in the edge cases, or b) tons of new tooling (because existing tools won't take these steps for you).

That is... until you try to remove a submodule.

I like sobmodules, but the whole feature needs a lot more polish before it's widely adopted.

That's fair. I think the important thing is to be able to have multiple versions of portions of your repo and then be able to version that. A branch of branches, so to speak.