Because why should they be able to trademark any word combination of "<Some word>Doom<OtherWord>" ? How would this make the world a better place for others if companies could claim any word that somehow contains or resembles their trademarks as their own?
I mean it’s not their trademark to enforce. Is just having “Doom” in part of your name enough to confuse people with the game? I think not, especially because this isn’t even a video game.