2023 Xgames averaged 459,000 viewers.
not sure what tennis matches you are asking about. both events are cheaper to produce than a season of football.
both events are annual one offs, not months long seasons spread across the country that the networks are themselves sponsoring.
UFL, outside of St Louis, can't get any fans to show up to the games. Now that the networks are league owners, they will feel the heat directly. XFL alone lost 60 million just in 2023.