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It's not necessarily that the writng of the story was flawed, but merely that the viewer was distracted by a subplot less important than the main plot, to the point that their disappointment is mostly due to nitpicking the details that thye cared more about, with some justifications caused by the writing.
There's Just Here for Godzilla, where the viewer only watches a work for one specific aspect that's not the main focus of the story.
There's also Come for the X, Stay for the Y, where the viewer is attracted to a work because of one aspect, but remains hooked because of an entirely different one.
Just Here for Godzilla is close, but what I'm looking for is a viewer's reaction to/interpretation of a work that results because of the Just Here for Godzilla mentality they have to a certain subplot.
So sometimes a viewer watches/reads something and picks up an interests on a certain subplot. Whether it's due to the way the story was presented or something about the viewer themselves, that subplot becomes the focus of the viewer's attention for the rest of the story. So as the story reaches its conclusion and wraps up, the viewer is left wondering, "Hey, what about...? Get back to that! That was so important!", and all while failing to acknowledge what they had actually been reading/watching because they were too distracted by their interest in that one subplot.
Is there a trope for this phenomenon?