Clinton thought she could just sort of coast through the summer and fall and win the election. She doesn’t even have the stamina to give a concession speech.
Or the manners. Or the class. She's always held the American public in contempt, including those who voted for her and for Bubba, so now that she's suffered the bitterest disappointment possible, why should she bother to thank the people who worked so hard for her? She may be in hysterics, she may be having mini-seizures, she may be too depressed to speak coherently--there are plenty of possibilities. None of them reflects positively on her.