Australia

Possibly. Rightly or wrongly, there's quite obviously a social stigma around these breeds that deters potential owners. And small dogs will always be more popular due to their relative affordability, perceived safety around small children and likelihood of being accepted by a landlord/strata group.

The stigma also plays in the opposite way - people who want a dog for defence are more likely to select one of these breeds. These owners are likely not as concerned with the emotional well being and/or safety of the animal. They're more likely to surrender or abandon them for a replacement if the animal proves too difficult to manage or doesn't live up to expectations.

I don't know if these breeds have the potential to be safer, or if they should be banned (I would like to see detailed and peer reviewed research into these areas) but I do know there a lot of reasons why you see the dogs you do on the RSPCA adoption website.