This is the problem. They will not “let go”, mentally, which leads to the physical.
Pit-bull-dog types are tenacious. They don’t want to give up the fight. They were bred for that (long before terrier was introduced - it was already in the bulldog type; the T just added more surefire tenacity). That’s what the name is for - fighting bulls (the nastiest heavy animals you could find). Mere dog-fighting came later. Normal dogs will let you have it and then let go, unless you step in again for a fight. The dog’s “warning” didn’t work in that case.
It CAN be bred out of the types, but it has to be a concerted effort over generations. Original Bulldogs today and Bull Terriers and Boston Terriers have had it basically bred out of them. But their relatives kept fighting.
For now, PBTs and the same types are genetically inclined for these problems, as surely as they are for the particular head shape.
the only bully dog I think is really mellow almost all the time (ie every single day of every single one of their lives...) is the American Bulldog. Always really laid back - from what I’ve seen.
There seem to be more and more lab attacks, maybe its overbreeding.