I'm not surprised by the results. I don't see why there's such a debate here.
No female tennis player at the moment draws big ratings or attendance.
Maria, only draws money to/for herself. You can watch a multitude of WTA/ATP events in the early rounds across the world, and the men's matches are full, and the women's matches, including Maria's are bone empty. I point that out all the time, to many peoples chagrin here. Same for the ratings. Maria doesn't help them. That's a fact. So this NBC ratings report is really not a surprise. And it would be the same in many other countries across the world, as well; not just the US.
Just because Maria has the ability to make money for herself, it doesn't mean that she makes money for the sport. She doesn't.
She's certainly not Michael Jordan, Tiger Woods, Lebron James, Magic Johnson and Larry Bird-like, etc., who helped increase ticket sales, publicity, and ratings, transcending their sport. Maria doesn't do that. And no amount of endorsement money she makes on her own is going to change that. I think people confuse those two aspects. Making money for yourself, is not the same as helping and transcending your sport. She's just not there (despite what many of her fans think).
It's kinda like the JLo syndrome. People liked her enough to talk about her, and what clothes she wore, but weren't willing to spend the money to support her movies, records and TV shows. Cause if you look at her track record for her movies and records, most of them did not do well (you can easily search her name in Boxofficemojo.com if you don't believe it), especially when you consider their promotional and production budgets. She was a relative disaster sales wise.
Now back to these ratings. I think something else may need to be considered. There could be a large portion of the population, that is turned off by Maria's grunting, and just refuses to watch (though of course they could of turned the sound down). That shouldn't be forgotten as well. There's a large contingent of tennis fans, who absolutely hate Azarenka and Sharapova. Obviously Sharapova is not grunting on photo shoots and when she's promoting products. Think about that?
But until things change (whether it's new or renewed rivalries, a dominant new/young or consistent champion), women's tennis, allover the world, is just not that popular to begin with. And many fans, seem to hold too large of an opinion of what they feel their players worth (especially if they feel their glamorous) and value is on the tennis court.
Didn't someone try and argue once that she was bigger than Michael Jordan becasue he asked his roomates who Michael Jordan was and they didn't know who he was?