A large part of that is because there are so many 'pit bulls' that there are irresponsible owners or breeders who are breeding for aggression, training for aggression, and not socializing their dogs.
A large part of that is because there are 'bully' breeds that are derived in whole or in part from breeds that were once used to bait bulls and bears, and thirty-five years of breeding for bad traits has undone a hundred years of breeding for good traits.
A large part of that is because while there is only one Pit Bull (the American Pit Bull Terrier), there are three breeds recognized as pit bulls by most professionals (American Pit Bull Terriers, American Staffordshire Terriers, and Staffordshire Terriers), and four breeds by others (American Pit Bull Terriers, American Staffordshire Terriers, Staffordshire Terriers, and American Bulldogs), and more than a dozen breeds or mixes mistakingly identified by the police or media as 'pit bulls' in initial reports that later turn out to be something other than an American Pit Bull Terrier, American Staffordshire Terrier, Staffordshire Terrier, or American Bulldog.
We DO have a 'pit bull' problem. However, when you looks at the deaths caused by Rottweilers, Chows, Malamutes, or Huskies, you're looking at a single breed. Then you look at the deaths caused by 'pit bulls,' you're looking at deaths primarily caused by four breeds and mixes, with another dozen breeds responsible for one or two deaths.
We DO have a 'pit bull' problem, but 'pit bull' is a catch-all phrase just like AR-15 or AK-47.
The reason pits are a pooled group (type) of dogs is because they share ancestry. I think the term is Molossor dogs (an agressive guard dog) was used as a foundational breed for a group of dogs that share agression problems because they were bred to be agressive. This very old ancestry is core and key to the pit bull problem - they were never bred to be companion dogs, they were bred to kill. They do not fit in civil society - their attacks and silent approach, hunting people etc. are not like domesticated dogs. I don’t believe that the problem is irresponsible owners - not when you have different breeds of dogs resulting from common breeding stock all having agression issues. I have yet to see decades of breeding for “good traits” if we are talking about companion dogs. There’s alot of wishful thinking on the part of those who either own or know dogs that never went postal. The problem is there’s no way to tell them apart - I used to believe as you did but then I started watching videos, reading accounts, talking to people who loved their pits but had to give them up (or worse) - it is the breed. The “irresponsible owners” thing doesn’t account for enough bodies but it sure doesn’t help.
Pit bull is a term used to describe the problematically agressive group of genetically related breeds that were bred for agression. Now we can’t tell a “good pit” from a “lethal pit” until the ambulance arrives. I wish it were otherwise, but it is not.