XL bullies/American Bulldogs/‘Mastiffs’ - let’s face it, a lot of these dogs come under very vague descriptions.
A big part of the issue here IS the owners, I don’t think anyone denies that - these bred types are (obviously not exclusively) largely owned by people ill-suited to keep dogs of this size, strength and temperament - and all too often by those with substance use issues too - and kept in heavily built up areas with little or no garden. I would assume this is another part of the difference in how they are perceived in other countries.
Still, it doesn’t negate the issue that for years these people have also kept other large breeds without the issues we are seeing now. There is an issue with this breed, for whatever reason. Pocket bullies won’t be much better either, not least because many are so deformed that they will be in constant pain.