I don't know if I'm correct with what I understand (correct me if I'm wrong), but I don't think we would be happy to pay to use bitsy. Afterall, it isn't a very complex engine for making huge games.
Yes, it is a very limited resource and if we had to buy a license then we would not use the service. However, that is not what we were asking. We were asking if we can make a game in the engine and then sell the game. A license of some sort is required most of the time for engines like this one and some engines can be used free of charge via a creative commons license.