They’re not really taking the money. They get a cut from the sales, but the money goes to the developer. They’re just earning money from having the marketplace/store from transactional tax. So quality is probably not their responsibility.
I mean, you could have the mod being sold at ORBX central, or Aerosoft, or SimMarket at the same time. But if the quality is bad, then it would be equally bad regardless of where you get it from.