According to kernel.org git does not store all the permissions possible for files.
Git is a content tracker, where content is de facto defined as
“whatever is relevant to the state of a typical sourcecode tree”.
Basically, this is just files’ data and “executable” attribute.
So git stores only the content in the file and the execute bit.
(This is probably a design choice. Probably driven partly by the fact that not all file systems are the same.)