IIRC, part of the issue is that XL Bullys in the UK have a very shallow gene pool, and are massively inbred. Apparently over half are descended from a US dog, 'Killer Kimbo' (who himself was the result of mating a brother and sister).
Kimbo's descendants are responsible for multiple fatalities in the US, to the point that most American US XL Bully breeders avoid using any of his bloodline. In quite a few of the cases, the dogs involved in serious injuries and fatalities seemed to be placid, loving family dogs that just suddenly snapped one day.
In the UK, the XL Bully gene pool is a lot smaller, where breeders (back when it was legal) were breeding from dogs where Kimbo was the singular great-grandparent, and both grandmothers were sisters.
I absolutely love dogs, but XL Bullys, particularly in the UK, are (through no fault of their own) inbred genetic time bombs that are liable to explode. I hate to say it, as I'm sure that there's ones that would live blameless lives, but I think a humane cull would have been safer.
And honestly, I wouldn't be against dog licences, with mandatory training. It'd protect the dogs as much as (if not more than) people.