Well, the actors were getting paid, just not in money. The actors obviously decided it was worth the experience and publicity to invest their time. That's why

Well, the actors were getting paid, just not in money. The actors obviously decided it was worth the experience and publicity to invest their time. That's why the acting trade is so hard to get in to. There are thousands of people willing to supply their skills for free. The supply vastly outweighs the demand.