Why should Bethesda get anything at all? Unless they're going to the trouble of making sure their official patches don't interfere with popular mods or something like that, they aren't providing additional value beyond providing the game that was already paid for. I think one of the issues in this wasn't just that mod creators would have gotten a small fraction of profit, but because Bethesda's behavior was somewhat rent-seeking -- attempting to normalize publishers getting a cut of sales that they hadn't gotten before, for doing no extra work.