That's a good question. I would think that modern ships should scream "collision course ahead" with light, sounds, etc. However, psychologically, maybe it's believed that this would make people even _more_ complacent? I don't know, just speculating. Never the less, the captain should never allow his sailors to think, "we're almost there, we're in friendly waters, we can relax". No, always on alert. It's unforgivable.

Of course the cargo ship has BNWAS installed. The captain might have turned it off? If the bridge personnel didn't know about the (no-AIS, running dark, much faster) navy boat, however, their wakefulness wouldn't have prevented the end result.