Maybe he sold the cards as being unlimited money for 30 minutes. It's probably not even difficult to refresh the cards. He was already in their system, he had the account numbers, it could have been scripted. This was a one-shot deal -- the accounts and his hole into WorldPay were probably cut-off the next day. There's little reason for him not hype these cards, sell them for a good price and keep them working.
The benefit to him is his increased reputation. You can't survive in these circles unless people vouch for you. That's why, when you read articles about darkmarket, they talk about reviewers who inspect products from vendors. This guy just sold products that netted $9,000,000. Everyone is going to want to buy from him now.
Don't think that there's nothing in it for the vendor. ATM skimmers sell for $7,000. If he pulls this off again, people may just buy the cards from him for $10,000 each for a 700% return. That's not too shabby for sitting on your ass and not taking the risk of being on the streets.
I just don't believe that this was structured like a traditional gang. This level of organization in online fraud is completely unprecedented. There were more than 6 cities hit in numerous countries, I don't see them recruiting that many random people to participate and having profit sharing since gangs are tight-knit.