Mostly for exposure and showcasing what a specific seller can do.
However, if you sell high-quality, nicely prepared and packaged models, you have nothing to worry about. Customers, more often than not, seek quality, and free models do not always fall into that category. If a person chooses a free model over a premium model, chances are he would not have paid for a model in the first place. At least, that's what I believe.
https://hackemtu.com/