Git doesn't see the contents of the folder installed via composer, how to add it to git?

Question

git

Good afternoon! Installed an extension for yii2 - yii2-user . I added it to composer.json, then I did a composer update, everything was installed. But when I wanted to commit the changes, I found that git added the vendor/dektrium/yii2-user folder, and there are no files inside this folder, because it does not see them. I looked in .gitignore, there is nothing about this folder. The extension was added not like a submodule, what could be the reason?