Why does bitch have such a negative connotation?

Bitch simply means female dog. I’ve had the honor of owning two female dogs in my life (I’m mostly a cat person). Both were wonderful, loving companions. How did the word come to be treated as a verb for complaining and criticizing constantly; and a noun for a bitter, nasty-tempered woman? Sure, if you treat a dog badly enough, they might develop a mean streak. But that goes equally for dogs of either gender, doesn’t it? So isn’t it a bitch that bitches got stuck with such a negative connotation when it’s really human behavior, not canine, that’s being pilloried?