They're not working for free though. If you are a wedding photographer the value in saying "I did all the photographs for season X of <stupid but very popular w

They're not working for free though. If you are a wedding photographer the value in saying "I did all the photographs for season X of <stupid but very popular wedding show>" has huge monetary value. If the supply/demand economics were such that you still had to pay them $stipend/minimum wage/premium this would still be the case. Photographers are free to accept in-kind payment or not.