At least three reasons off the top of my head:
1. The publicity sells the producer as someone who can make you money. Kinda like an investment adviser or hedge fund does.
2. The publicity conveys to some parts of the potential audience that others thought this was a show worth seeing. It's a metric of word of mouth.
3. Advertising quality assumes you have some to advertise.
Thanks for making such a well-reasoned, succinct, and cogent explanation. I had been trying to craft a response, but you expressed it so much better than I ever could.
