I have a somewhat different perspective on this. I use my own models, purchased models & free models in my compositions. I sometimes credit model sources & sometimes don't. It depends on how prominent the model is in the overall composition or how many I've used. I tend to use models as a form of primitive object. I distort them, apply booleans to them, texture them in unusual ways, etc. & use them in ways that often make them unrecognizable. In that context, if I have obtained the models in a legal way (either through purchasing them or because they were given away by their creators without strings attached) & I am not violating copyrights, I don't feel I'm morally obligated to credit every model I use every time. It would also be a tedious task to keep track of the models I use in each composition - I view creating art as play & that would make it more like work.

That said, I do periodically credit modelers whose work has become an important input to my own, just out of gratitude. And for those who use models in a more straightforward way & that feature them prominently in their completed work, it does make sense to credit them.

"Every child is an artist. The problem is how to remain an artist once we grow up." - Picasso