Size of FBX in AssetBundle is larger

Hello, everyone! I got meshes in FBX files, average size of one fbx on my HDD is 250-500 kb. After building an AssetBundle EditorLog writes that sizes of fbx’es a more larger. And AssetBundle’s size is big. Why is this happening?

how much more bigger?
the bundle it self may contain more stuff then the fbx files.
also, the system file size not always the same like the real size file if you are using drive compression for example.