Lets not anthropomorphize canine reproduction. A male dog is acting instinctually. Doing what he needs to do to reproduce when HE thinks the time is right. With or without human interference he is still going to try - if a bitch is resistant he may have a challenge on his hands. Male dogs do NOT stand there contemplating or have the moral judgment to decide what is right or wrong. That is the difference. There could be dozens of reasons a female DOG is not willing or ready. Could be reasons they know, could be reasons breeders know, could just be the nature of the 'beast'.