There are several categories of Bad Fiction.
Category 1: This is the sad mediocrity. The prose is often functional, but bland. The plot is functional, but bland. Often it has the feeling of being done for money or obligation, and thus suffers for it. Occasionally fun to to read if one doesn’t have anything better, but not fun to talk about.
Cat 2: This is the kind of bad fiction that’s heartfelt but terrible. There’s more sincere effort then Cat 1 Bad Fiction. But it’s still ultimately bland. These are generally sloppy amateur projects with bad prose. Most bad fanfiction falls into this category.
Cat 3: This is the sort of bad fiction that has effort behind. Lots and lots of real effort. Now, maybe the effort is a sort of ‘draw a tree but miss the forest utterly’ effort on worldbuilding for its own sake and details. Maybe most of the effort is spent arguing about the work rather than working on it. Maybe all of the above is true. Category 3 Bad Fiction often has just enough technical competence to not be dismissed outright.
I try to focus my Bad Fiction Spotlights on Category 3 Bad Fiction.