As a full on dog person, I've owned, trained, dealt with aggression problems and done work at breeding kennels, with owners it's most lack of knowledge with lots of breeders is money ..
Breed anything so long as it makes money that's where the designer dogs come in, cross two breeds call it a flash name
Designer dogs regardless of their names are crossbreeds which used to be called a mongrel.
(A mongrel dog or mutt is made up of a mix of breeds – generally three or more. It might be the offspring of two cross breed dogs, with a background of four breeds, or it might be that you have no clue or only a vague idea of the breeds your dog comes from)
The cost of some can be mind blowing and finally, when a puppy's ancestors include two or more breeds, many of their genes may be conflicting.
For example, suppose puppies are bred from dog breeds that has genes for friendliness. Another has genes for standoffishness. Another has genes for aggression. When the puppies inherits a jumble of conflicting genes, you don't know which genes will "top" the others or which ones will blend together to form some intermediate result.
These Bully XL are of no use to themselves or the people that buy they are bred to fight, before these it was the Pitt Bull and after the XL they will bred something else becasue puppies go for £3500 plus and while that is the case the suffering of others dog or perosn will be of little consequence to those reaping the harvest of profit.
As a dog person the sooner something is done the better for all our sakes, our kids and our own dogs.