Cinema 4D unfortunately does not export all needed information in OBJ format. The OBJ standard requires a .MTL file, along with the .OBJ file, to specify texture locations, colors, etc. C4D does not export a .MTL at all unless you have an add-on/plugin that handles OBJ export better. You would see the same lack of texture issue if you loaded the model in any other program, perhaps even if you load it again in C4D (the OBJ version after export). This is an unfortunate limitation of C4D.
You might try exporting as some other format that and then convert using PoseRay (free tool), Assimp, Meshlab, Deep Exploration, or other 3D model converter...
- Oshyan