And if sports are wasteful, all forms of entertainment are. Why do you think like that? The thoughts in my mind are not so precious to the world that it shouldn't be distracted by 'useless' entertainment, and I guess neither is yours.
Yes, of course there are a few other things to talk about, but even "news and weather" is dangerous, because some think Louisiana is currently showing us the future of global warming, and others think it shows that people who choose not to insure their property should not be rewarded with a bail out, lest there be moral hazard.
Sports is the safe bet.
Of course friends can discuss whatever they want. But in less familiar company, one may want to avoid topics that can lead to disagreements. Politics and religion being the classic examples.
Or, as the Professor told Eliza: "Stick to the weather, and everybody's health".
I would assume that once the two people get to know one another the window of safe topics would become broader
For example, if I state gymnastics isn't a sport, just as ballet isn't, and that watching it means condoning child torture, is that a safe bet?
(Edit: and that's ingoring the really contentious subjects such as whether England really scored that third goal in 1966)
Or electronic gaming? Where are the League events? The Olympics are in Rio, but everyone's watching Seattle for the DOTA 2016 International tournament.