Would you agree that small dogs get away with bad behaviour more than larger dogs?
They could lunge, bark, charge at other dogs and because they cannot do as big a damage as a larger dog on average, they get away with a lot of bad behaviour.
Either the owners don't see it as a major issue or other dog owners think their own dogs can hold their own so they let it go.
But if a larger dog or certain breeds did the exact same thing, people will be up in arms and are more likely to get reported.