Typically if you do a closeup of a computer screen in a movie/TV there's a specific action the user is performing or message they've received that is important

Typically if you do a closeup of a computer screen in a movie/TV there's a specific action the user is performing or message they've received that is important to the plot. You want that message to be big and obvious enough that in the 1.5 seconds of footage of the screen, it's obvious to an engaged watcher what is being done. Real UIs rarely make one thing so much huger than everything else on the screen that it will immediately draw attention as fast as the film needs you to, so they make up their own.