Because a lot of dog owners are ignorant cunts, that's why. Many people get a dog and then wish they could turn it on and off like some toy when they don't want to deal with it. That's not how it works, you have to raise your dog almost like a child. It takes a lot of time and effort to properly socialise a dog, especially stronger breeds because smaller dogs have a natural aversion to them and will automatically go on defensive near them.



Back home where my cavvie still lives with my mom there are a lot of bully breeds around and most are extremely well socialised and play well with smaller dogs. But there are 2 or 3 that I would never allow near my dog or small children, and guess what, one look at their owners and you know why that is the case.