Pal, you're comparing Nintendo franchises with Five Nights at Freddy's. All of the games you describe are completely different games, completely different genres in fact. Dr. Eggman and Bowser are bombastic, unrealistic supervillains from kid-friendly franchises. William Afton is a serial killer. Those two things aren't comparable.

He killed 10 kids

Because portraying William Afton as some sort of sympathetic figure would harm his character as opposed to these PG Nintendo franchises you're mentioning

Not all villains need to have redeeming qualities, y'know?

The difference. Is that bowser isnt doing it because he wants eternal life. In literally most adaptations where he kidnaps peach, hes doing it because he literally just loves peach.

Eggman also doesnt just flat out murder children.

Ganondorf again also doesnt just murder children.

Henry didnt betray him. And henry isnt going to hell. As i believe he most certainly would go to those pearly gates.

Instead of comparing William to enemies like Bowser.

Compare them to people like Freddy Krugar. Michael myers. etc.

And you could say he did actually have a redeeming quality. Some evidence does show he did care about his children.

He just lost that redeeming quality when his children die.

Also. Not every villain needs a redeeming quality. Otherwise the evil they committed is undermined.

William Afton does it because when he was a kid he was bullied by children, so he vowed to kill every child and decided to use pizza to lure them. I think scott Car thorn confirmed this