This happens a lot in horror - the need to provide reasons. Probably the most egregious example for me is the way Thomas Harris was forced into developing a backstory for Hannibal Lecter (Nazism again), who was so effective a villain in Red Dragon and The Silence of the Lambs because he was simply inscrutably evil - almost like the devil in human form. There was no reason for it except that he was evil for evil's sake. There seemed something especially compelling about that - somebody who was perfectly sane and yet chose to be bad - so the explanatory backstory was particularly ill-judged.
It goes without saying that part of the reason why Lovecraft is so important is that he (sometimes - this gets overblown) eschewed explanations. Explanations render horror knowable and as soon as one gains knowledge of something the fear of it diminishes.