Here's a thought. Obsession strikes me as the more likely. Is obsession "natural"? Perhaps it is, as part of the overall spectrum of human behavior.
I want to offer the possibility that the "Hard Core Size Queen" when taken to the furthest extreme may be an expression of a rare type of "body dysmorphia". It may be an unusual form of disturbed body awareness, part of the spectrum of psychological categories that include anorexia nervosa and types of OCD. I'm just guessing, as I have no background in this.
The unusual part here is the requirement for a partner's body fitting the disturbed view of what is desirable, in this case the penis size, to such a degree that pain is welcomed as a prerequisite, and that there is potentially an irresistable rationale to move on if a larger penis is available.
If it was merely size, then fisting could easily rival even the "King" in any scenario, but it has to be a real penis, it seems.
On the positive side, thank goodness there are women and men who want to partner with the freakishly large male. From what I have observed here it can be quite frustrating and difficult for the male who is too large for most people, and who complain here that they seldom actually achieve intercourse or maintain ongoing relationships.
On the negative side, if one of those gigantic guys (who has a difficult time in the first place because of the limitations due to his size) gets chosen or dumped for strictly physical reasons, he must be sorely disappointed to encounter this type of fickleness.
Body Dysmorphic Disorder