The lack of ratings has a few causes. Nobody's gone to a game for more than a year, it diminishes fan interest. People are struggling financially, and frivolous things like sports can be put on the shelf for a long while. The players individually are as good as ever, but the concept of 'team' is really a joke anymore. The best players seem to change teams every few years, no real fan loyalty is developed.
You know who Magic played for. You know who Jordan played for. You know who Isaiah played for. You know who Bird played for. And Kobe, and Duncan...... You know who you grew up with. They had fiercely loyal fans. Sure some guys moved around, but it was the exception. Lately its all different.
Who did Shaq play for? Lebron? Durant? Harden? Kahwi? They played for everyone. Think their former fans still adore them?
It just affects fan interest to a greater degree than the NBA masters think it does.