Cowardice, laziness, and obliviousness. If somebody doesn't jump in to at least attempt to stop a situation like this, it's because they're afraid something will happen to them, they don't have time for it, or they simply just couldn't give a shit. That's all it is. It's extremely difficult to force bravery and effort into people and I think sharing this video won't do anything. The people who did get up and do something either were acting on instinct or knew that something bad might happen. But they tried to do something anyways, and that's admirable. (To me anyways.) Bullying can never be 100% eradicated, it's a fact by this point. However, walking away like nothing happened (or recording it, like srsly wtf) doesn't help the situation.
I've seen probably well over 50 scenarios like this but only ever stepped in once. And I probably sound like an ass when I say this, but I think sometimes (depending on the situation and the participants) it may be better to do nothing at all. If I was ever getting bullied I would never in my life want somebody to step in. That'd make me feel so useless and weak. I'd much rather endure whatever form of bullying than have somebody else feel sorry for me.
All in all, my opinions are split on this. I'm still not certain of what I'm supposed to do whenever I see things like this.