@IMACOP
It's not that the authors of these stories forget that the games "no action" endings are bad endings, it's that we play games as the heroes/heroines so in our minds the story is supposed to have a good ending for us.
The "heroine" (not the MC) in this story is actually a good example of what you're saying: she thinks that the story is set in stone and doesn't act on it taking everything for granted and doing so she actually get the bad ending.
On the other end, the MCs in these isekai stories are good, kind, loveable characters that experienced the story as the heroines and get reincarnated in the villainesses so they act in a way that (in their denseness) doesn't change the good outcome for the main characters and/or the world ('cause they're good heartead and love the world/characters/story) while at the same time gettings things better for themselves (since villainesses generally end up dead/exiled/poor) and in doing so they change everything.
These stories are basically all about villains trying to ruin themeselves 'cause they're actually good persons and in doing so obtaining the "bad ending" (from the heroine POV).