adding nested .git folders inside .gitignore

Question

This question shows how to use .gitignore to ignore various locations of bin folder inside your project. I've tried the same but with .git folder. I've put .git/ inside my .gitignore then run git init and then git add . but with no luck. Git still complains about adding another repo inside current repo. My goal is to create one big repo which will contain multiple other repos (I do not need their git history, just files). I know about best practices and git modules etc. I'm just curious why it does not works with .git/ but it works with bin/

EDIT I' do not know what I did wrong at the time of writing this post but now it seems that it is working. I have empty .gitignore and if I issue git status there is no mention about .git folders. This also confirms git ls-files (which I've issued after git add . and git commit). But if I rename those .git folders e.g. to .git.tmp then git status start to "see" them. This behavior is also described in this post. My git version is 2.25.1