Steps to reproduce :

- open the project attached by the user in his last reply
- open the scene
- export it as a package
- create a new project and import the package
- notice that the textures are missing

Why it is not going to be fixed?
When Unity imports a .obj file it uses the FBX SDK to load the file. When the FBX SDK reads the .obj file it will also read the .mtl for creating the materials.

Unity does not know anything about this dependency between the .obj and the .mtl, so when exporting a package we do not include the .mtl file and thus when importing the package in a different project the material settings are lost.