Confirmation bias at work. We as humans look for meaningful patterns in everything and often seek out patterns that fit preconceived notions. When we find them, we run with them even if the pattern wasn't actually there to begin with. We want something to be true so we create a way to make it true.
"I want stun guns for my toon but I am not getting them. Because I favorited them, the drop rates must have been lowered, it is the most logical explanation." Erroneous and illogical but oh so many people buy into the pattern.