Are you serious? Janet has sold over 100 million albums worldwide, making her one of the highest selling music artists of all time. Her real success comes from music, not acting, she also loves music too much to stop. She might just be taking a little break to gather new material and come back in a bigger way.
The reason she wasn't sold as much as she used to is partly because her music has been as good and partly because she doesn't promote it a whole bunch like others do. Also, a part of it might be that stupid Super Bowl thing, which really isn't a big deal, especially when you see how female artists today prance around in nothing.
Music is in her blood, she can only stop for so long