There's a principle at stake here
It's the same one that says rape victims should not be accused of provocation because of what they were wearing "Don't use the Internet" .... REALLY? "Don't wear a short skirt, or you're just asking for it"
However, I'm not surprised people don't want to get involved. A friend of mine once intervened in a bloke getting pushed around on a tube platform one night. The original victim ran away and *he* ended up getting a good kicking.