You know why, William ?? Bad breeding.
Back in the '70's cocker spaniels were all the rage. Everybody wanted one. So anybody that had two cockers put them together and had a litter of pups. Didn't matter if the two dogs had any business passing along their genes or not. There was a big demand and good money in cocker spaniel pups. So we ended up with a high-strung, spazzy and often downright mean breed from what had once been a loyal, hard-working bird dog.
Same thing, to a slightly lesser degree, happened with Labs a decade or so later.
Now it's Pit bulls. I see it every day. They are not only the choice of the ghetto but of the college student. How many times I have delivered to a freshman, just moved in, and they've proudly got their Pit bull pup in the apartment. Poor thing spends the majority of its life in a cage alone in the apartment. Couple years later the dog is ramming the other side of the door when I knock. Kid graduates, the real world kicks in and Door Rammer ends up at the shelter waiting for adoption by someone who knows NOTHING about how the dog was raised/neglected. Makes for a bad combination whether it's a Pit or a poodle. But currently it seems the it is the dog of choice for neglect.