Because the term “space monster” better encompasses the ridiculousness of the concept : that unphotographable space aliens are traveling through a fold in the space-time continuum and are abducting schizophrenics to study their lower intestines.
Just a kind of tweaky handle, trademark, I think.
Soeething distinguishing that one can fantasize results in one sounding more intellectual and erudite . . . compared to the ignorant serfs that believe such stuff . . . LOL.
Trouble is . . . those with an experience need never be at the mercy of those with only an argument and intellectual fantasies and tweaky labels.