For games like American Football, there's only 11 actual minutes of action, but it takes 3+ hours to complete the game[0]. That leaves a lot of time to watch a second screen.

[0]: https://qz.com/150577/an-average-nfl-game-more-than-100-comm...

Second screening even in things like drama is very popular.

If you're watching a sports game, I can see that having a second stream (perhaps curated) with easy to access stats on that game, or a different angle to what the director thinks you want, or whatever.

I don't see the appeal of second stream in drama, but in things like sport, yes