I thought of this article when I read your post.
https://deadspin.com/nba-ratings-nosedive-proves-sports-are-not-essential-1844718626
Basically, it rejects the common claimed reasons and proposes the real reason is people have found other **** to watch or do.
Man, what a terrible article. Mainly because he said this about the theory that politics were hurting viewership: "Obviously these are not persuasive arguments in any sense, but rather compelling reasons to stick a railroad spike through one’s own head." and then followed up with a reasonably long article without any argument to support his claim that it was something else.
I'm obviously skeptical that the politics are the dominating reason that interest is dropping, but it'd be interesting to see some data. Survey data or even just showing how other forms of entertainment that used to dominate (like late night TV and prime time network television) have seen their share of the ratings suffer as more options became available. I suspect that's largely what has happened, except that sports for whatever reason were immune to the same fate until people realized how easily they could go without, and it's a combination of COVID and injecting politics that made a lot of people realize quicklly that they don't really need or even like sports as much as they thought, at least compared to the alternatives available to them.