This is why I cannot hate you:
It takes too much wasted energy and bitter determination to hate properly. Hate has to be fed, constantly. You cannot let it lapse even for a moment because that single instance of clarity will show you just how futile and silly it is.
It takes a dogged single-mindedness to hate persistently. You need to put aside your rationality and dismiss the possibility that you may ever be wholly happy again. You have to sacrifice the good for the bad.
And hate makes you ugly. That, is just not acceptable.
This is why I cannot hate you. It is simply too much to ask.