It be like that

That's because just knowing the rules doesn't mean that a person can "instinctively" incorporate them into their interactions. It certainly doesn't help that humans are hardwired for pattern recognition. When someone doesn't meet the "standard" for "normal" social interactions that our brains are subconsciously looking for it raises all kinds of flags. Now none of this means we shouldn't be consciously making an effort to temper our instinctual responses but it does explain a little bit. Imagine being slapped, except without the pain, randomly while trying to hold a conversation with someone. It's not that you can't do it, it just takes an effort. Many just don't want, need, or care to make the effort.