Addition: When I import the created SMD into Blender again, it looks correct.

Hey, I'm pretty new to GMod modding and wanted to use a "custom" model for a new addon. For this I took an existing Blender model that already uses several shader textures. Now when I export the model, it is just gray - why is that?

Sorry if this is a stupid question... here are the pictures:
https://imgur.com/a/wbVbT8n