Why was it not shown how Diggory, Krum, and Delacour defeated their dragon for the egg?

Question

Here is the scene where Harry Potter is battling the Hungarian Horntail for the egg:

Why wasn't it shown how Diggory, Krum, and Delacour defeated their dragon for the egg?

Answer 1

Quick answer: Drama. We're more emotionally invested in Harry, and it's the first time we've seen the Task.

Longer answer: In the books, we mainly follow Harry. A scene without him in is very rare. We learn things at the same time as he does, and mainly see everybody else from his point of view, and share his feelings. This has transferred to the films as well.

In-universe, it's probably so they don't get an unfair advantage in seeing what other competitors have done. In terms of effect on the book/film audience, it heightens the drama, and we go through that period of waiting and worrying with Harry. The scene is treated a bit differently in the film, but the reason behind filming it like that uses the same rationale, so I'll use book quotations.

Harry is left alone in the tent, with us — we're not getting any previews. We start to feel as worried as Harry does, because he's the only emotional source from the story we have. If you saw this scene from the audiences' perspective, you'd probably have excitement as well, and by the time Harry gets out there, you've seen the other three succeed, so would probably expect Harry to as well.

"You're to go in here with the other champions," said Professor McGonagall, in a rather shaky sort of voice, "and wait for your turn, Potter.

[...]

It was worse than Harry could ever have imagined, sitting there and listening. The crowd screamed. . . yelled. . . gasped like a single many-headed entity, as Cedric did whatever he was doing to get past the Swedish Short-Snout. Krum was still staring at the ground. Fleur had now taken to retracing Cedric's steps, around and around the tent. And Bagman's commentary made everything much, much worse. . . . Horrible pictures formed in Harry's mind as he heard: "Oooh, narrow miss there, very narrow". . . "He's taking risks, this one!". . . "Clever move - pity it didn't work!"

[...]
He felt much more aware of his body than usual; very aware of the way his heart was pumping fast, and his fingers tingling with fear. . . yet at the same time, he seemed to be outside himself, seeing the walls of the tent, and hearing the crowd, as though from far away.

[...]
He stood up, noticing dimly that his legs seemed to be made of marshmallow. He waited. And then he heard the whistle blow. He walked out through the entrance of the tent, the panic rising into a crescendo inside him.

_{Harry Potter and the Goblet of Fire - Chapter 20: "The First Task"}

It also means we see the arena through Harry's eyes — we go there with him, and it gives us that direct connection to his feelings again..

And now he was walking past the trees, through a gap in the enclosure fence.

He saw everything in front of him as though it was a very highly coloured dream. There were hundreds and hundreds of faces staring down at him from stands that had been magicked there since he'd last stood on this spot. And there was the Horntail, at the other end of the enclosure, crouched low over her clutch of eggs, her wings half-furled, her evil, yellow eyes upon him, a monstrous, scaly, black lizard, thrashing her spiked tail, heaving yard-long gouge marks in the hard ground. The crowd was making a great deal of noise, but whether friendly or not, Harry didn't know or care.

_{Harry Potter and the Goblet of Fire - Chapter 20: "The First Task"}

In the book, how the other champions managed is just a quick sentence from Ron. Harry doesn't really mind — he's feeling "elated" and is waiting to get his scores, and is just pleased that Ron believes him. He isn't really interested in how the others did, so it doesn't get much focus.

"You were the best, you know, no competition. Cedric did this weird thing where he Transfigured a rock on the ground. . . turned it into a dog. . . he was trying to make the dragon go for the dog instead of him. Well, it was a pretty cool bit of Transfiguration, and it sort of worked, because he did get the egg, but he got burned as well - the dragon changed its mind halfway through and decided it would rather have him than the Labrador; he only just got away. And that Fleur girl tried this sort of charm, I think she was trying to put it into a trance - well, that kind of worked too, it went all sleepy, but then it snored, and this great jet of flame shot out, and her skirt caught fire - she put it out with a bit of water out of her wand. And Krum - you won't believe this, but he didn't even think of flying! He was probably the best after you, though. Hit it with some sort of spell right in the eye. Only thing is, it went trampling around in agony and squashed half the real eggs - they took marks off for that, he wasn't supposed to do any damage to them."

_{Harry Potter and the Goblet of Fire - Chapter 20: "The First Task"}