Has the bar been raised too high for Serena?
Probably Screamerova and the Belgians have raised the bar in women's tennis too much for Serena to be competitive on the highest level any longer. Upcoming players aren't afraid anymore, MaScrea and the Belgian are their role models and they know how to cope with Serena. Tennis is another game now compared to the early 21st century (when Willy sisters dominated). The game has moved on! Today's players are athletic AND are able to keep the ball in the field on a constant basis.
BTW, Serena's multiple off-court interests (the design company, her Hollywood career, philantropy) don't help either. And we must not forget the ankle injury from last year!
Is her time over?