Satanism stems from an enlightenment era conception of Satan, not the medieval. In the satanic temple’s case they also adopt some of the more classic imagery as a way to push against Christianity when it oversteps its bounds. The more grotesque image of satan eorks perfectly for this as it’s much easier to show the hypocrisy with than any other I’ve encountered.

Side note: as far as i know, god is the only character in the bible that already has, and has promised to again destroy the world. Satan (which translates to the accuser or adversary) has mostly just questioned god and tested peoples faith. So cutting away the popular notions from centuries later actually puts satan in a much more favorable light.