I think this depends if you view a game or league purely as a compition (per definition if one team wins, another one has to lose), or as a "brand": very exciting games can increase the popularity of a league/sport, increasing revenue/attention even for the losing team.
I think most sports fans only look at the first part.
Teams A and B play each other, and everything gained by A is lost by B and vice versa. A zero-sum game. But somehow we have a fan X. But why are they interested? It seems like some extra value is created by the interaction of A and B (entertainment). This means it’s not a zero-sum game.
It’s not some games that increase the popularity of a sport. It’s all games. A lot more people show up to a stadium on game day than an off day.
If it’s zero-sum, how can a team with a losing record continue to operate indefinitely?