Basically, they just don't want their brand Doom to be associated with the band "progressive thrash metal" music.
It's not the first time this happens and it does make sense. In another occurence about a podcast named Garden of Doom, they found an agreement.
> Jeff, who tried to trademark Garden of Doom, his podcast, says he came to an agreement with the lawyers representing Id Software; he says he just can’t make a movie or video game called Garden of Doom.