Resale brokers charge the seller a 10%-15% commission for handling the sale. If they allowed the buyer to pay with a credit card, the 2-3% fee they would owe the credit card company would reduce their commission to as low as 7%, a 30% reduction in what they make on the sale. Given those figures, it's not surprising that most resale brokers do not accept credit cards.
It's different when you purchase directly from Disney because the profit margin is much larger so they are more willing to give up 2-3%. And given the volume of business Disney does with the credit card companies they probably get a discounted rate from the credit card companies.