It's my contention that TV ratings are down for sports because they've turned off a substantial part of their fanbase by venturing into the political realm which this posting will cause so I'll leave it at that. 
That's probably some factor. Depends on the sport maybe. I think hockey was probably down due to the team in the Finals. NFL ratings are down but not as much as others. Game 6 of the NBA Finals competed against Sunday Night Football. Last night game 7 against Alabaman/Georgia. Tonight Sunday night football against another MLB game 7. These choices never happen in a normal year.
Would be ineteresting to see someone publish stats about total sports viewership. I would say that with more sports on more people were watching sports in August-October than other previous year during that time.
NFL ratings against previous years once MLB is over would be a good comparison in November/January.
Here is a Forbes article.
https://www.forbes.com/sites/tommybeer/2020/10/15/nbas-ratings-drop-not-due-to-blowback-over-players-activism-poll-suggests/#276ff53b6b31"According to SportsMediaWatch, the drop in sports ratings comes amidst a widespread decline in television viewing overall, as an "average of 76.2 million viewers were watching primetime television on the first five nights of the Finals, nearly eight million fewer than during last year's Finals." While only 3.8 million Americans were tuned in to the "big three" cable news networks on the first five nights of the 2019 NBA Finals, 8.4 million viewers were watching those same three cable news channels in 2020. Still, over the 41 nights that basketball playoff contests were played this summer, the NBA delivered television's highest rating among adults aged 18-49 on 30 of those 41 nights. That 18-49 demographic is extremely important to advertisers."
