So, yes. But 
… I blame “community”. Hehe.
Basically, the model product type is intended to be purely geometrical data and a strictly validated clean geometry meeting production requirements, like naming conventions, topology validations, uvs, etc. But there have been many cases where users wanted to bring along the materials for whatever reason.
And since the model was intended to be the model product type for your production there are ways to allow shaders/looks to come along in certain integrations, just because there was a request for it.
I’m not pushing hard against it, I’m just not using it. To everyone their own (to the extent it makes sense as a studio/production-specific toggle).
In Maya for example it can publish a ‘look’-like representation with model products to easily build a look dev scene from any temp materials applied in a model scene.