Why is C not considered an 'object-oriented' language?

Question

It seems that C has its own quasi-objects such as 'structs' that can be considered as objects (in the high-level way that we would normally think).

And also, C files themselves are basically separate "modules", right? Then aren't modules kind of like 'objects' too? I'm confused as to why C, which seems so similar to C++, is considered a low-level "procedural" language where as C++ is high-level "object-oriented"

*edit: (clarification) why and where, is the line drawn, for what an 'object' is, and isn't?