Because it totally needs it.
You know, way back in "A New Hope", that first film (which
was called Episode IV).
The bad guys show they mean business. They show us that the Death Star is operational. They show it blowing up a planet for goodness' sake!
If, on the other hand, we'd never seen that example, the audience would be denied the fear and thrill of knowing, absolutely, how dangerous the Death Star is. We need to see how frightening something can be, otherwise it's all simply theoretical.
That's why the Daleks exterminate an extra, early in the piece. To SHOW us the danger The Doctor and his companions are in.
Yeah, those are pretty nerdy examples. OK, let's look at Samuel L Jackson. In his words (and I'm paraphrasing) he used to read scripts and see his character get killed off. Because his character was there to serve as a warning for others. He has died in 18 movies.
As Jackson's star rose, he began to live to the end credits (way to go!). Then something weird happened. In films to come, his characters started dying again. (Like being eaten by a shark in Deep Blue Sea). He wondered why, and the director said "Because if your character can die, that means anyone can die."
And now of course I can't find the link. But hey, it's just an example, OK?
The reason I'm talking about this is because *drumroll* I DID NOT HAVE A DEATH STAR MOMENT IN ONDINE 4.
I am so disappointed in me.
I knew there was something 'not working' in the story, and it would come to me eventually and then I'd work it out.
Now I have. I need to bring in a metaphorical Death Star, show how it works, have the worst thing happen. THEN our plucky heroes can get to work restoring peace in the galaxy.
So when you're writing a story, have a big think: What's the worst thing could happen?
Make it happen.
Then make it all right again.