I reckon everyone would love to own a perfect dog. And in the perfect world all dogs behave the same, perfectly stable and socialised. But there's no perfect dog without enough training, and training needs enough commitment, time and dedication. People will only train their dogs to the level where they're sufficiently satisfied and unfortunately the threshold level is different between small dog and big dog.
A nip to the hand by a small dog would (sadly) be tolerated by the owner, while a nip by a big dog will flare the red alarm. There's greater urgency for big dog to understand manners, since if they don't, they'll probably get dumped by their owners. There are more big dogs out there waiting in the kennels than small dogs.
I have respect for people in this forum who try their best to teach and learn with dogs, no matter the size.