Git submodules are fine and can be really useful, but they are really hard. I've run into problems like:
1. Git clone not cloning submodules. You need `git submodule update` or `git clone --recursive`, I think
2. Git submodules being out-of-sync because I forgot to pull them specifically. I'm pretty sure `git submodule update` doesn't always work with this but maybe only when 3)
3. Git diff returns something even after I commit, because the submodule has a change. I have to go into the submodule, and either commit / push that as well or revert it. Basically every operation I do on the git main I need to also do on the submodule if I modified files in both
4. Fixing merge conflicts and using git in one repo is already hard enough. The team I was working on kept having issues with using the wrong submodule commit, not having the same commit / push requirements on submodules, etc.
All of these can be fixed by tools and smart techniques like putting `git submodule update` in the makefile. Git submodules aren't "bad" and honestly they're an essential feature of git. But they are a struggle, and lots of people use monorepos instead (which have their own problems...).
