Why did they change the whole story for Doom?

Question

They were supposed to be fighting Demons from hell not genetically mutated humans...! It's still a great movie but it drifted too far from the games, there's too much in common for them to have changed stuff like that...

It completely is different from the game though, there's a real big difference between accidentally opening a portal to hell and discovering a mutation, that's my whole point, they could've stuck with the demons and had a different place or something and it would've been alright but...

Answer 1

To make it more realistic, like that's possible.

Answer 2

just think it as sequel, or altered ending