There are ways to collect necessary operational fees without needing to turn a profit, and it's also to operate a digital marketplace on the communities own collect infrastructure, so that might not even be necessary.
Amazon exists as a big monopoly marketplace because they started collecting a large number of goods they were selling for profit and then leveraged that momentum and near monopoly into controlling the whole market. But it started out as just a retailer. For digital goods, we can create digital marketplaces that aren't controlled by one of the retailers in that market.
