Live sports ratings are down across the board; and the 2 driving factors are non-basketball related. For all sports/shows there’s a core audience and casual audience. The casual audience drives the peaks in ratings.
One of my uncles is a casual MLB fan, who hasn’t watched a second of MLB because of the lack of fans in the stands, which completely changes the viewing experience for the casual observer. He’s an example of one segment of viewers turned off by this.
The other factor is the closing/partial reopening of the bars, clubs, in-restaurant dining, and other places where casual audiences are only watching because it’s preferred viewing in those places.