Why? Cause she isn't fit and confident?
Fit, confident and skilled.
However, I would say the more the latter two (confident and skilled).
Remember, Petra played similarly in Montreal and New Haven (at least the hitting with more topspin--deep, in the corners, with angles, and the good defense part) during the humid NA summer, post Olympics. And I know you haven't felt she been fit all year.
Now, if you remember--during last years YEC, Petra played Linz before it. Right?
Petra was a hot mess her first two matches during Linz. And the Eurosport announcers (particularity the male broadcaster--rather melodramatically I'd say), killed Kvitova. Now Petra was getting her game together, after recently slumping and a lay off (kinda like now---though obviously not slumping nearly as bad, compared to this time last year).
However, by the time she played her last three matches at Linz (Dannie, Jankovic, Cibulkova), Petra played some of the best tennis I'd seen her play--skill wise. She was an absolute all court beast; arguably better than Wimbledon!! She was playing a perfect combination of skill, patience and aggression in my opinion. Loved it/her!
Now, barely anyone saw it (and she didn't beat the top 10, for those that didn't see it--though Jankovic played vintage offensive/defensive Lady Jaja tennis). But I was very confident (based off what I seen), and even stated so--here on TF. Yes! She looked that good and excited me that much with her play. Petra was just "Magnificent!"
Of course/luckily, her Linz form carried into the YEC and Petra won the Damn thing--undefeated. Can Petra reacquire that form during practices with pre and post pubescent boys at Prostejov, or wherever she is?
.......Don't know (as I SMH).