It's all about balance. Private venues want their customers to have the best experience they can so they will want to come back. The purple lanyard solution MIGHT work, depending on the ratio of people wearing them and the number of people filming. Or it might be that lots of people want to film and the one guy with the purple lanyard keeps getting in the shot and ruining it. Or it might be too many people want to film and end up ignoring it. But in the best case, it allows youtubers to make their videos while not requiring those who don't want to be in them to stay home, as non-customers.