It costs disney nothing to do this. They will use an existing space that is not being used currently so nothing lost. They will offer some snacks and beverages for free and they will have CMs working there but the costs of those things will be charged back to DVC and paid for through member dues.
As far as Disney already having their money, it’s not really how they would or should think of it. The money paid upfront is gone. Disney got credit for that revenue years ago, It has no financial benefit to Disney today. The money they want today from DVC owners is money spent on park tickets and dining and merchandise. They still want to attract members to come to WDW and visit the parks and spend more money. They also want satisfied customers. I don’t have any official statistics but it’s not uncommon for DVC owners to buy more points over time. They aren’t going to do that if they are unsatisfied with the product. So if Disney decided to just stick it to them because they “already have their money” they would be missing out on a lot of future revenue from a loyal customer base. That’s bad business.