The Rock is one of the biggest celebrities in the world. A guy like him has to be on 24/7 or else, the very first time he's caught being unprofessional, the public will run with it and he'll get the reputation of being an a$$hole. John Cena is the company man. Wherever he goes, he represents WWE's brand as an ambassador while being one of the few wrestlers that can be recognized outside of wrestling. He can't afford to be an a$$hole because of his public image.
Sasha's never had the profile or magnitude of those two, and even then, she's outside of her job. If she was refusing to sign autographs or tried skipping out on taking pictures with fans, it would be one thing. But she's not obligated to pay attention to the fans because they want her to. A wave would've been better, but the thing with people like that is they believe they own these celebrities because they're famous and they're fans of them. They forget that they're human and might not always want interactions like that. Even with The Rock, I remember reading somewhere on here that fans are kept away from him when he's rehearsing/filming to prevent him from getting distracted. When all that is done and he's not currently doing anything, he acknowledges them.
You want an autograph, go to the signing. But don't wait in the blistering cold for someone for four hours and be surprised when they say no.