Why did the Armageddon (1998) plot require a "rogue comet that jarred loose a Texas-sized asteroid"? [closed]

Question

Wikipedia's Armageddon (1998 film); Plot begins:

A massive meteor shower destroys the orbiting Space Shuttle Atlantis, before entering the atmosphere and bombarding New York City. NASA discovers that the meteors were pushed out of the asteroid belt by a rogue comet that jarred loose a Texas-sized asteroid that will impact Earth in 18 days, causing an extinction level event that will wipe out all life on the planet. NASA scientists plan to drill a deep shaft into the asteroid and plant a nuclear weapon into it that, when detonated, will split the asteroid into two halves that will fly safely past Earth.

Surprisingly the accepted answer to Do astronomers generally agree that the distinction between comets and astroids is not so clear? begins

If we're going to get technical, Asteroids are not really an official name anymore.

But in 1998 it was certainly still believed that asteroids and comets were clearly distinct and different types of objects. I don't remember anything about there being a comet that dislodged an asteroid in the film. Why was this complication introduced? Why did the Armageddon (1998) plot require a "rogue comet that jarred loose a Texas-sized asteroid"?

Answer 1

It may not be exactly as shot, but the text I grabbed from a copy of the script says:

GOLDEN Okay guys, one of the worst days in N.A.S.A history just got worse. Ten million to one. A rogue comet came from deep space and collided with an asteroid. Some kids actually got a picture of the collision event and told no one. The stuff that hit this morning was the collision's forward-thrown matter, mere pebbles from what's about to come. Walter?

So this explains why there is a precursor cloud of higher-speed debris traveling ahead of the rock itself. If it were a comet, an extra-solar visitor or a long-period Earth-crossing asteroid, any associated fragments would be traveling at the same speed as the rock itself. So there needs to have been a collision to generate fast debris.

Further, a collision between two orbiting asteroids wouldn't be at a high enough relative velocity to throw one entirely out of its population and drop it on the Earth. Gravitational perturbation by a major body like Jupiter, while it could conceivably fling an asteroid at Earth, wouldn't generate the high-speed initial wave of debris. So it has to be something pretty big traveling at a high relative speed that hit the asteroid.

At the time the movie was shot there weren't any demonstrated rocky interstellar visitors like ʻOumuamua, so it's likely they just assumed the only reasonably massive object that would cross orbits to collide with an asteroid is a comet. They do hit things occasionally, like Schumacher-Levy 9.