I don’t know whether not paying a Standing Order costs Nationwide money (my instinctive response is no - it would be stupid for them to incur costs for something they control) but Monzo doesn’t need to make money through those sorts of charges & doesn’t want to because users hate them.
Tom commented recently on how simple it is to reject a scheduled payment &..it’s very simple, for a bank that’s built using a modern technology stack at least.
Instead, here’s my summary of how they’ll make money - it’s amazing what you can do with a much lower cost base -