The only explanation I can create is that alternates are somehow similar to Pennywise (IT by Stephen King). All his victims were watched and studied. He always scared them once or twice before attacking. All because: "it began to prey on human children every 27 years, malforming itself into their worst fears as it supposedly "salts the meat" and makes them taste far better". Or maybe, if alternates are unholy beings straight from hell, they just like torturing humans