Not everyone is built like Arnold and I don't know that many Bruce Lees in real life. It seems the bad guy managed to take the victims by surprise here. And though the victims did have a little time to react (calling 911) it seems pretty clear that they were overpowered quickly and failed to put themselves together to fight back for whatever reason.

At close range, a strong, motivated (high on drugs, psyched up or whatever) guy with a knife intent on cutting you apart is a lethal proposition. Bare hands vs. knife is a really bad idea. I've only done a little training in that direction but at least it was enough to dispell many common illusions. Especially when you realize that 95% of traditional blocks and disarms do not work under stress. Simply put, if you find yourself unarmed at close quarters against a motivated knife fighter you will most likely die. Unless you get very lucky or the bad guy makes a dumb move.

Without knowing the details of the incident, the bad guy may not even have needed to put a knife on one of the victims' throat to force the others into submission. Looks like they panicked and they certainly didn't believe they could defeat the bad guy, which is probably why they rather jumped through the window (basically commited suicide).

If they thought they couldn't defeat the bad guy, they were right. You can't win a fight if you don't believe in yourself. So the victims may well have lost the fight before it even started.