Does the LL know they have a pitbull or even a dog? I knew people who had two pitbulls there (fox point), but the landlord was just absentee (it was pet free) and from my experience I'd be willing to guess half of those large breed dogs you're spotting aren't approved on the lease. Same thing my partner experienced renting in Brookline: everyone had a dog because management just cashed checks and let the building fall into disrepair lol.

Agreed, though, its a property insurance and liability issue for many owners to take on.

edit: not advocating lying what-so-ever. Neither of us has ever had a pet, it was just an open secret that others in the building were not approved since it was strictly against the lease