I have never read any of the 50 Shades books, and this answer is solely based on the many times I have read reviews and commentaries that denigrate the writing quality. So take that into consideration when reading this answer.
As I understand it, the series was written as a piece of fan fic originally. There really are no prerequisites for an author of fan fic beyond having an idea, and taking the time and energy to write it out. So, it is completely possible that the author of the 50 Shades series does not have any formal training in how to construct a narrative.
By no means am I suggesting that authors of fan fic don't know how to write, just that they may be less likely to have been educated about structural issues that create effective narrative. And i don't know anything specific about the background of the author, who may or may not have any formal training in writing fiction.
But I bring this up because it may be that you are looking to analyze elements within the novel that simply aren't there. There may be no pinch point, because she didn't know that creating one would be useful to drive a plot.
As I understand it, the appeal of these books is the sexual relationship/content between he two main characters, and it is very possible that they were able to appeal to a great number of readers on the basis of that content alone, even without the formal elements that usually form the framework of a successful story.
It's very like the cliche of a pizza delivery guy coming to the door in a porn movie and then being drawn in to have sex with his customers. That has got to be one of the silliest plot elements ever, but most people don't watch porn movies because they have good plots.
TL;DR-- you may not be able to identify all of these structural elements in this novel, because the author, untrained in formal writing practice, may not have included them in the first place.