My hot take: glTF adoption is so slow because it does a lot of things people don't need it to do. 

I need the skinned 3D model and the animations. I don't particularly like to put the texture on the 3D file.  

But what i'm sure i don't want to put there are physics objects, lights and totally not cameras. 

I guess it makes sense for importing from blender to maya, but i don't want that appearing in my engine.

I would still be using obj if it was open.