Note: This post contains spoilers for Amazon's Invincible.
In this case, the "why" refers to the end of the first episode. Nolan Grayson, aka the all powerful alien superhero Omni-Man (voiced by J.K. Simmons), is a member and leader of the hero team Guardians of
the Galaxy the Globe. Out of nowhere, Omni-Man turns against his fellow heroes and brutally murders them all. He's not a benevolent protector like the real life hero he's based on: he's a plant for the Viltrumate race, and they're on their way to conquer Earth.
According to Kirkman, the Omni-Man reveal was something the writers knew would arrive early, unlike how it played out in issue seven of the comic. The staff had thought about it for episodes two and three, but then Kirkman began to write the pilot, and he knew what to do. "That would really be the best way to end the first episode," Kirkman recalled. "Here's the premise, oh by the way, the premise is completely different at the end of the episode!" Moving events around is nothing new for Kirkman, who was more than happy to suggest what characters should die to the writers of the Walking Dead series, based on his comics. Those urges have since died down for Invincible. "It's a well worn path that I've traveled down in comic book form," he noted, "I think I've gotten a little bit better at adapting my own material."
There's an irony that comes from the panel, as Kirkman was joined by cast members Ross Marquand, Lauren Cohan and Lennie James. Cohan and James respectively voice War Woman and Darkwing, and Marquand pulls double duty as The Immortal and Aquarius. (You can probably guess which superheroes these characters are based on.) The trio of Walking Dead alums -- Marquand and Cohan's characters Aaron and Maggie are on the main show, where James' character Morgan also began before being transferred to the spinoff Fear the Walking Dead -- were contacted by Kirkman before official channels reached them. "I remember saying, 'yeah, sure, excellent,', " laughed James, "and not really thinking about it." Speaking the words sans any real context was something like a leap of faith, but James trusted Kirkman to get him through it.
That trust backfired on the cast, thanks to the fact they recorded lines in 2019. Seeing their characters get murdered and cut down in 2021 was quite a shock, and James' reaction was so strong that he ran to the other room to tell his wife about his death. But in an alternate world where the Guardians got to live? If the actors have anything to say about it, they're chilling and living life. "I'd like to infiltrate the high school somehow," Cohan mused, "She’d be a guardian at work, keeping tabs on teenage drug use." Marquand thinks The Immortal would be big into theatre. And Lennie? "Darkwing would kill all the other Guardians," he professed. In his mind, the dark hero would do the impossible: finally pull a twist on Kirkman.