They were created in America using the American Pitbull Terrier as the foundation and various other breeds to bulk out the dogs.
The APBT is actually a medium sized, athletic looking dog. To get to the bully they added in American Bulldog, Great Dane, Dogo Argentino, Mastiffs.
They became very popular very quickly, with a certain kind of person and like all things, demand initially outstrips supply so they become even more sought after. They became the it-dog with celebrities, footballers, wannabe hard boys and other idiots, with dogs going for thousands and thousands. Because there weren't that any in the country, a good few were imported from America.
People of ill-repute saw an opportunity, linked to money laundering, drugs, and tax avoidance. Greeders saw an opportunity to make £50,000 per litter.
Now, when breeding dogs, especially of that size temperament should come first. If a dog shows any kind of nervous, anxiety, aggression etc, it should be removed from the breeding pool. Only healthy, physically and mentally, adult dogs should be bred from. Large dogs mature very slowly and some personality traits don't show until well in adulthood.
But with the bully, they were in such demand that people just focused on breeding for size and colour over anything else. It was not unheard of for 9 month olds to sire pups, being pups themselves.
So you've got dogs that when 5 or 6 would become human aggressive, nervous with children or unpredictable and they've already sired 60-70 pups, and their own pups have gone on to be bred from. Way too late to do anything.
And of course in this country, we don't do breeding licenses, so anyone can get a dog and breed it, sell the pups on to anyone, and who knows what happens to the dogs from then on.
The American Bully XL's sheer size means it is not suitable for an average UK home. They need a sizeable home, with space to run and and burn off energy. They need an owner dedicated to training, socialising and able to physically control them. They need an owner well versed in Canine behaviour and is able to recognise when the dog is acting up and do something about it. Not baby it, keep it in a small terrace and never walk it because the dog is too bloody strong for them. But that's exactly what they got. So the dogs weren't in the right homes where there needs were being met, meaning frustrated, anxious, neurotic dogs being kept in homes with humans way out their depth, or falling into the hands of people using them for intimidation, who also had no clue what they were doing. Even worse, kids dangling from their necks. Ticking time bomb.
As these mass produced pups started to mature we started to hear more and more about people being killed by them. I do believe they are more likely to bite than other dogs because of the genetic dumpster fire they were given but also, given their sheer size, a bite by an XL is going to be fatal very quickly. They weigh the same as an adult. Their heads and jaws are massive. They will do damage with a warning bite, if they mean business you will die.
But as ever, it's not the fault of the dogs. It's the fault of the humans breeding them, the owners who buy them and put them in their homes and our stupid government that could have tightened the laws on breeding, ownership etc on all dogs years ago but don't want to.